SUBORDER HETEROSOMATA
=THE Flatfishes.=—Perhaps the most remarkable offshoot from the order of
spiny-rayed fishes is the great group of flounders and soles, called by
Bonaparte _Heterosomata_ (ἔτερός, differing; σῶμα, body). The essential
character of this group is found in the twisting of the anterior part of
the cranium, an arrangement which brings both eyes on the same side of
the head. This is accompanied by a great compression of the body, as a
result of which the flounders swim horizontally or lie flat on the sand.
On the side which is uppermost both eyes are placed, this side being
colored, brown or gray or mottled. The lower side is usually plain
white. In certain genera the right side is uppermost, in others the
left. In a very few, confined to the coast of California, the eyes are
on the right or left side indifferently.
The process of the twisting of the head has been already described (see
p. 174, Vol. I). The very young have the body translucent and
symmetrical, standing upright in the water. Soon the tendency to rest on
the bottom sets in, the body leans to left or right, and the lower eye
gradually traverses the front of the head to the other side. This
movement is best seen in the species of _Platophrys_, in which the final
arrangement of the eyes is a highly specialized one.
In some or all of the soles it is perhaps true that the eye turns over
and pierces the cranium instead of passing across it. This opinion needs
verification, and the process should be studied in detail in as many
species as possible. The present writer has seen it in species of
_Platophrys_ only, the same genus in which it was carefully studied by
Dr. Carlo F. Emery of Bologna. In the halibut, and in the more primitive
flounders generally, the process takes place at an earlier stage than in
_Platophrys_.
=Optic Nerves of Flounders.=—In the Bulletin of the Museum of
Comparative Zoology (Vol. XL, No. 5) Professor George H. Parker
discusses the relations of the optic nerves in the group of flounders or
flatfishes.
In the bony fishes the optic nerves pass to the optic lobes of the
brain, the one passing to the lobes of the opposite side simply lying
over the other, without intermingling of fibers, such as takes place in
the higher vertebrates and in the more primitive fishes.
According to Parker's observations, in ordinary bony fishes the right
nerve may be indifferently above or below the other. In 1000 specimens
of ten common species, 486 have the left nerve uppermost and 514 the
right nerve. In most individual species the numbers are practically
equal. Thus, in the haddock, 48 have the left nerve uppermost and 52 the
right nerve.
In the unsymmetrical teleosts or flounders, and soles, this condition no
longer obtains. In those species of flounder with the eyes on the right
side 236 individuals, representing sixteen species, had the left nerve
uppermost in all cases.
Of flounders with the eyes on the left side, 131 individuals,
representing nine species, all have the right nerve uppermost.
[Illustration:
FIG. 427.—Young Flounder, just hatched, with symmetrical eyes. (After
S. R. Williams.)
]
There are a few species of flounders in which reversed examples are so
common that the species may be described as having the eyes on the right
or left side indifferently. In all these species, however, whether
dextral or sinistral, the relation of the nerves conforms to the type
and is not influenced by the individual deviation. Thus the starry
flounder (_Platichthys_) belongs to the dextral group. In 50 normal
specimens, the eyes on the right have the left nerve dorsal, while the
left nerve is also uppermost in 50 reversed examples with eyes on the
left. In 15 examples of the California bastard halibut (_Paralichthys
californicus_), normally sinistral, the right eye is always uppermost.
It is uppermost in 11 reversed examples.
Among the soles this uniformity or monomorphism no longer obtains. In 49
individuals of four species of dextral soles, the left nerve is
uppermost in 24, the right nerve in 25. Among sinistral soles, or
tongue-fishes, in 18 individuals of two species, the left nerve is
uppermost in 13, the right nerve in 5.
Professor Parker concludes from this evidence that soles are not
degenerate flounders, but rather descended from primitive flounders
which still retain the dimorphic condition as to the position of the
optic nerves, a condition prevalent in all bony fishes except the
flounders.
The lack of symmetry among the flounders lies, therefore, deeper than
the matter of the migration of the eye. The asymmetry of the mouth is an
independent trait, but, like the migration of the eye, is an adaptation
to swimming on the side. Each of the various traits of asymmetry may
appear independently of the others.
[Illustration:
FIG. 428.—Larval Flounder, _Pseudopleuronectes americanus_. (After S.
R. Williams.)
]
The development of the monomorphic arrangement in flounders Professor
Parker thinks can be accounted for by the principle of natural
selection. In a side-swimming fish the fixity of this trait has a
mechanical advantage. The unmetamorphosed young of the flounder are not
strictly symmetrical, for they possess the monomorphic position of the
optic nerve. The reversed examples of various species of flounders
(these, by the way, chiefly confined to the California fauna) afford
"striking examples of discontinuous variation."
A very curious feature among the flounders is the possession in nine of
the California-Alaskan species of an accessory half-lateral line. This
is found in two different groups, while near relatives in other waters
lack the character. One species in Japan has this trait, which is not
found in any Atlantic species, or in any other flounders outside the
fauna of northern California, Oregon, and Alaska.
=Ancestry of Flounders.=—The ancestry of the flounders is wholly
uncertain. Because, like the codfishes, the flounders lack all
fin-spines, they have been placed by some authors after the
_Anacanthini_, or codfishes, and a common descent has been assumed. Some
writers declare that the flounder is only a codfish with distorted
cranium.
[Illustration:
FIG. 429.
]
[Illustration:
FIGS. 429 and 430.—Larval stages of _Platophrys podas_, a flounder of
the Mediterranean, showing the migration of the eye. (After Emery.)
]
A little study of the osteology of the flounder shows that this
supposition is without foundation. The flounders have thoracic ventrals,
not jugular as in the cod. The tail is homocercal, ending in a large
hypural plate, never isocercal, except in degraded soles, in which it is
rather leptocercal. The shoulder-girdle, with its perforate
hypercoracoid, has the normal perch-like form. The ventral fins have
about six rays, as in the perch, although the first ray is never
spinous. Pseudobranchiæ are developed, these structures being obsolete
in the codfishes. The gills and pharyngeals are essentially as in the
perch.
It is fairly certain that the _Heterosomata_ have diverged from the
early spiny-rayed forms, _Zeoidei_, _Berycoidei_, or _Scombroidei_ of
the Jurassic or Cretaceous, and that their origin is prior to the
development of the great perch stock.
If one were to guess at the nearest relationships of the group, it would
be to regard them as allies of the deep-bodied mackerel-like forms, as
the _Stromateidæ_, or perhaps with extinct Berycoid forms, as
_Platycormus_, having the ventral fins wider than in the mackerel. Still
more plausible is the recent suggestion of Dr. Boulenger that the
extinct genus _Amphistium_ resembles the primitive flounder. But there
is little direct proof of such relation, and the resemblance of larval
flounders to the ribbon-fishes may have equal significance. But the
ribbon-fishes themselves may be degenerate Scombroids. In any case both
ribbon-fishes and flounders find their nearest living relatives among
the _Berycoidei_ or _Zeoidei_, and have no affinity whatever with the
isocercal codfish or with other members of the group called
_Anacanthini_.
[Illustration:
FIG. 431.—_Platophrys lunatus_ (Linnæus), the Peacock Flounder. Family
_Pleuronectidæ_. Cuba. (From nature by Mrs. H. C. Nash.)
]
The _Heterosomata_ are found in all seas, always close to the bottom and
swimming with a swift, undulatory motion. They are usually placed in a
single family, but the degraded types known as soles may be regarded as
forming a second family.
=The Flounders: Pleuronectidæ.=—In the flounders, or _Pleuronectidæ_,
the membrane-bones of the head are distinct, the eyes large and well
separated, the mouth not greatly contracted, and the jaws always
provided with teeth. Among the 500 species of flounders is found the
greatest variation in size, ranging in weight from an ounce to 500
pounds. The species found in arctic regions are most degenerate and
these have the largest number of vertebræ and of fin-rays. The halibut
has 50 vertebræ (16 + 34), the craig-flounder 58, while in _Etropus_ and
other tropical forms the number is but 34 (10 + 24). The common
flounders of intermediate geographical range (_Paralichthys dentatus_,
etc.) show intermediate numbers as 40 (10 + 30). The apparent
significance of this peculiar series of fact is given on page 212, Vol.
I. It is, perhaps, related to the greater pressure of natural selection
in the tropics, showing itself in the better differentiation of the
bones and consequently smaller number of the vertebræ.
[Illustration:
FIG. 432.—Heterocercal tail of young Trout, _Salmo fario_ Linnæus.
(After Parker & Haswell.)
]
[Illustration:
FIG. 433.—Homocercal tail of a Flounder, _Paralichthys californicus_.]
]
Fossil flounders are very few and give no clue as to the origin of the
group. In the Eocene and Miocene are remains which have been referred to
_Bothus (Rhombus)_. _Bothus minimus_ is the oldest species known,
described by Agassiz from the Eocene of Monte Bolca. In the Miocene are
numerous other species of _Bothus_, as also tubercles referable to
_Scophthalmus_.
On the testimony of fossils alone the genus _Bothus_, or one of its
allies, would be the most primitive of the group. If it be so, the
simpler structure of the halibut and its relatives is due to
degeneration, which is probable, although their structure has the
suggestion of primitive simplicity, especially in the greater approach
to symmetry in the head and the symmetry in the insertion of the ventral
fins.
[Illustration:
FIG. 434.—Window-pane, _Lophopsetta maculata_. Virginia.
]
Soles have been found in the later Tertiary rocks. _Solea kirchbergiana_
of the Miocene is not very different from species now extant in southern
Europe. No remains referable to allies of the halibut or plaice are
found in Tertiary rocks, and these relatively simple types must be
regarded as of recent origin.
=The Turbot Tribe: Bothinæ.=—The turbot tribe have the mouth large, the
eyes and color on the left side, and the ventral fins unlike, that of
the left side being extended along the ridge of the abdomen. The species
are found in the warm seas only. They are deeper in body than the
halibut and plaice, and some of them are the smallest of all flounders.
It is probable that these approach most nearly of existing flounders to
the original ancestors of the group.
Perhaps the most primitive genus is _Bothus_, species of which genus are
found in Italian Miocene. The European brill, _Bothus rhombus_, is a
common fish of southern Europe, deep-bodied and covered with smooth
scales.
[Illustration:
FIG. 435.—Wide-eyed Flounder, _Syacium papillosum_ Linnæus. Pensacola,
Fla.
]
Very similar but much smaller in size is the half translucent speckled
flounder of our Atlantic coast (_Lophopsetta maculata_), popularly known
as window-pane. This species is too small to have much value as food.
Another species, similar to the brill in technical characters but very
different in appearance, is the turbot, _Scophthalmus maximus_, of
Europe. This large flounder has a very broad body, scaleless but covered
with warty tubercles. It reaches a weight of seventy pounds and has a
high value as a food-fish. There is but one species of turbot and it is
found in Europe only, on sandy bottoms from Norway to Italy. In a turbot
of twenty-three pounds weight Buckland found a roe of five pounds nine
ounces, with 14,311,260 eggs. The young retains its symmetrical
condition for a relatively long period. No true turbot is found in
America and none in the Pacific. Other European flounders allied to the
turbot and brill are _Zeugopterus punctatus_; the European whiff,
_Lepidorhombus whiff-jagonis_; the topknot, _Phrynorhombus regius_; the
lantern-flounder, _Arnoglossus laterna_, and the tongue-fish,
_Eucitharus linguatula_, the last two of small size and feeble flesh.
In the wide-eyed or peacock flounders, _Platophrys podas_ in Europe,
_Platophrys lunatus_, etc., in America, _Platophrys mancus_ in
Polynesia, the eyes in the old males are very far apart, and the changes
due to age and sex are greater than in any other genera. The species of
this group are highly variegated and lie on the sand in the tropical
seas. Numerous small species allied to these abound in the West Indies,
known in a general way as whiffs. The most widely distributed of these
are _Citharichthys spilopterus_ of the West Indies, _Citharichthys
gilberti_ and _Azevia panamensis_ of Panama, _Orthopsetta sordida_ of
California, and especially the common small-mouthed _Etropus crossotus_
found throughout tropical America. Numerous other genera and species of
the turbot tribe are found on the coasts of tropical Asia and Africa,
most of them of small size and weak structure.
[Illustration:
FIG. 436.—_Etropus crossotus_ Jordan & Gilbert. Cedar Keys, Fla.
]
_Samaris cristatus_ of Asia is the type of another tribe of flounders
and the peculiar hook-jawed _Oncopterus darwini_ of Patagonia represents
still another tribe.
=The Halibut Tribe: Hippoglossinæ.=—In the great halibut tribe the mouth
is large and the ventral fins symmetrical. The arctic and subarctic
species have the eyes and color on the right. Those of the warmer
regions (bastard halibut) have the eyes and color on the left. These
grow progressively smaller in size to the southward, the mouth being
smaller and more feebly armed in southern species.
The largest of the family, and the one commercially of far greatest
importance, is the halibut (_Hippoglossus hippoglossus_). This species
is found on both shores of both oceans, north of about the latitude of
Paris, Boston, Cape Mendocino, and Matsushima Bay in Japan. Its
preference is for off-shore banks of no great depth, and in very many
localities it exists in great abundance, reaching a length of 6 to 8
feet and a weight of 600 pounds. It sometimes ranges well out to sea and
enters deeper waters than the cod. The flesh is firm, white, and of good
quality, although none of the flatfishes have much flavor, the muscles
being mostly destitute of oil. Small halibut, called "chicken halibut,"
are highly esteemed.
Dr. Goode states that the "history of the halibut fishery has been a
peculiar one. At the beginning of the present century these fishes were
exceedingly abundant on George's Banks; since 1850 they have partially
disappeared from this region, and the fishermen have since been
following them to other banks, and since 1874 out into deeper and deeper
water, and the fisheries are now carried on almost exclusively in the
gullies between the off-shore banks and on the outer edges of the banks,
in water 100 to 350 fathoms in depth.
"The halibut with its large mouth is naturally a voracious fish, and
probably would disdain few objects in the way of fresh meat it would
come across. It is said, however, to feed more especially upon crabs and
mollusks in addition to fish. These fish 'they waylay lying upon the
bottom, invisible by reason of their flat bodies, colored to correspond
to the general color of the sand or mud upon which they rest. When in
pursuit of their prey they are active and often come quite to the
surface, especially when in summer they follow the capelin to the shoal
water near the land. They feed upon skates, cod, haddock, menhaden,
mackerel, herring, lobsters, flounders, sculpins, grenadiers, turbot,
Norway haddock, bank-clams, and anything else that is eatable and can be
found in the same waters.' Frequently halibut may be seen chasing
flatfish over the bottom of the water. About Cape Sable their favorite
food seems to be haddock and cusk. A very singular mode of attacking a
cod has been recorded by Captain Collins, an experienced fisherman and
good observer. They often kill their prey by blows of the tail, a fact
which is quite novel and interesting. He has described an instance which
occurred on a voyage home from Sable Island in 1877: 'The man at the
wheel sang out that he saw a halibut flapping its tail about a quarter
of a mile off our starboard quarter. I looked through the spy-glass and
his statement was soon verified by the second appearance of the tail. We
hove out a dory, and two men went with her, taking with them a pair of
gaff-hooks. They soon returned, bringing not only the halibut, which was
a fine one of about seventy pounds weight, but a small codfish which it
had been trying to kill by striking it with its tail. The codfish was
quite exhausted by the repeated blows and did not attempt to escape
after its enemy had been captured. The halibut was so completely engaged
in the pursuit of the codfish that it paid no attention to the dory and
was easily captured.'
"The females become heavy with roe near the middle of the year, and
about July and August are ready to spawn, although 'some fishermen say
that they spawn at Christmas' or 'in the month of January, when they are
on the shoals.' The roe of a large halibut which weighed 356 pounds
weighed 44 pounds, and indeed the 'ovaries of a large fish are too heavy
to be lifted by a man without considerable exertion, being often 2 feet
or more in length.' A portion of the roe 'representing a fair average of
the eggs, was weighed and found to contain 2185 eggs,' and the entire
number would be 2,182,773."
Closely allied to the halibut are numerous smaller forms with more
elongate body. The Greenland halibut, _Reinhardtius hippoglossoides_,
and the closely related species in Japan, _Reinhardtius matsuuræ_,
differ from the halibut most obviously in the straight lateral line. The
arrow-toothed halibut, _Atheresthes stomias_, lives in deeper waters in
the North Pacific. Its flesh is soft, the mouth very large, armed with
arrow-shaped teeth. The head in this species is less distorted than in
any of the others, the upper eye being on the edge of the disk in front
of the dorsal fin. For this reason it has been supposed to be the most
primitive of the living species, but these traits are doubtless elusive
and a result of degeneration.
_Eopsetta jordani_ is a smaller halibut-like fish, common on the coast
of California, an excellent food-fish, with firm white flesh, sold in
San Francisco restaurants under the very erroneous name of "English
sole." Large numbers are dried by the Chinese for export to China. A
similar species, _Hippoglossoides platessoides_, known as the
"sand-dab," is common on both shores of the North Atlantic, and several
related species are found in the North Pacific. _Verasper variegatus_ of
Japan is notable for its bright coloration, the lower side being largely
orange-red.
In the bastard halibuts, _Paralichthys_, the eyes and color are on the
left side. These much resemble the true halibut, but are smaller and
inferior as food, besides differing in details of structure. The
Monterey halibut (_Paralichthys californicus_) is the largest of these,
reaching a weight of sixty pounds. This species and one other from
California (_Xystreurys liolepis_), normally left-sided, differ from all
the other flounders in having the eyes almost as often on the right side
as on the left side, as usual or normal in their type. The summer
flounder (_Paralichthys dentatus_) replaces the Monterey halibut on the
Atlantic Coast, where it is a common food-fish. Farther south it gives
way to the Southern flounder (_Paralichthys lethostigma_) and the Gulf
flounder, _Paralichthys albigutta_. In Japan _Paralichthys olivaceus_ is
equally common, and in western Mexico _Paralichthys sinaloæ_. The
four-spotted flounder of New England, _Paralichthys oblongus_, belongs
to this group. Similar species constituting the genus _Pseudorhombus_
abound in India and Japan.
[Illustration:
FIG. 437.—Halibut, _Hippoglossus hippoglossus_ Linnæus. Marmot I.,
Alaska.
]
=The Plaice Tribe: Pleuronectinæ.=—The plaice tribe pass gradually into
the halibut tribe, from which they differ in the small mouth, in which
the blunt teeth are mostly on the blind side. The eyes are on the right
side, the vertebræ are numerous, and the species live only in the cold
seas, none being found in the tropics. In most of the Pacific species
the lateral line has an accessory branch along the dorsal fin. The genus
_Pleuronichthys_, or frog-flounders, has the teeth in bands.
_Pleuronichthys cornutus_ is common in Japan and three species,
_Pleuronichthys cœnosus_ being the most abundant, are found on the coast
of California. Closely related to these is the diamond-flounder,
_Hypsopsetta guttulata_ of California. _Parophrys vetulus_ is a small
flounder of California, so abundant as to have considerable economic
value. _Lepidopsetta bilineata_, larger and rougher, is almost equally
common. It is similar to the mud-dab (_Limanda limanda_) of northern
Europe and the rusty-dab (_Limanda ferruginea_) of New England.
[Illustration:
FIG. 438.—Wide mouthed Flounder, _Paralichthys dentatus_ (L.). St.
George I., Md.
]
The plaice, _Pleuronectes platessa_, is the best known of the European
species of this type, being common in most parts of Europe and valued as
food. Closely related to the plaice is a second species of southern
Europe also of small size, _Flesus flesus_, to which the name flounder
is in England especially applied. The common winter flounder of New
England, _Pseudopleuronectes americanus_, is also very much like the
plaice, but with more uniform scales. It is an important food-fish, the
most abundant of the family about Cape Cod. The eel-back flounder,
_Liopsetta putnami_, also of New England, is frequently seen in the
markets. The males of this species have scattered rough scales, while
the females are smooth. The great starry flounder of Alaska,
_Platichthys stellatus_, is the largest of the small-mouthed flounders
and in its region the most abundant. On the Pacific coast from Monterey
to Alaska and across to northern Japan it constitutes half the catch of
flounders. The body is covered with rough scattered scales, the fins are
barred with black. It reaches a weight of twenty pounds. Living in
shallow waters, it ascends all the larger rivers.
An allied species in Japan is _Kareius bicoloratus_, with scattered
scales. _Clidoderma asperrimum_, also of northern Japan, has the body
covered with series of warts.
[Illustration:
FIG. 439.—Eel-back Flounder, _Liopsetta putnami_ (Gill). Salem, Mass.
]
In deeper water are found the elongate forms known as smear-dab and
flukes. The smear-dab of Europe (_Microstomus kitt_) is rather common in
deep water. Its skin is very slimy, but the flesh is excellent. The same
is true of the slippery sole, _Microstomus pacificus_, of California and
Alaska, and of other species found in Japan. _Glyptocephalus
cynoglossus_, the craig-fluke, or pole-flounder, of the North Atlantic,
is taken in great numbers in rather deep water on both coasts. Its flesh
is much like that of the sole. A similar species (_Glyptocephalus
zachirus_) with a very long pectoral on the right scale is found in
California, and _Microstomus kitaharæ_ in Japan.
=The Soles: Soleidæ.=—The soles (_Soleidæ_) are degraded flounders, the
typical forms bearing a close relation to the plaice tribe, from which
they may be derived. There are three very different groups or tribes of
soles, and some writers have thought that these are independently
derived from different groups of flounders. This fact has been urged as
an argument against the recognition of the _Soleidæ_ as a family
separate from the flounders. If clearly proved, the soles should either
be joined with the flounders in one family or else they should be
divided into two or three, according to their supposed origin.
The soles as a whole differ from the flounders in having the bones of
the head obscurely outlined, their edges covered by scales. The
gill-openings are much reduced, the eyes small and close together, the
ventral fins often much reduced, and sometimes the pectoral or caudal
also. The mouth is very small, much twisted, and with few teeth.
[Illustration:
FIG. 440.—Starry Flounder, _Platichthys stellatus_ (Pallas). Alaska.
]
The species of sole, about 150 in number, abound on sandy bottoms in the
warm seas along the continents, very few being found about the Oceanic
Islands. The three subfamilies, or tribes, may be designated as broad
soles, true soles, and tongue-fishes.
=The Broad Soles: Achirinæ.=—The American soles (_Achirinæ_), or broad
soles, resemble the smaller members of the turbot tribe of flounders,
having the ventral fin of the eyed side extended along the ridge of the
abdomen. The eyes and color are, however, on the right side. The eyes
are separated by a narrow interorbital ridge. In most of these forms the
body is broad and covered with rough scales. The species are mostly less
than six inches long, and nearly all are confined to the warmer parts of
America, many of them ascending the rivers. A very few (_Aseraggodes_,
_Pardachirus_) are found in Japan and China. Some are scaleless and some
have but a single small gill-opening on the blind side. The principal
genus is _Achirus_. _Achirus fasciatus_, the common American sole, or
hog-choker, is abundant from Boston to Galveston. _Achirus lineatus_ and
other species are found in the West Indies and on the west coast of
Mexico. Almost all the species of _Achirus_ are banded with black and
the pectorals are very small or wanting altogether. All these species
are practically useless as food from their very small size.
[Illustration:
FIG. 441.—Hog-choker Sole, _Achirus lineatus_ (L.). Potomac River.
]
=The European Soles (Soleinæ).=—The European soles are more elongate in
form, with the ventral fins narrow and not extended along the ridge of
the abdomen. The eyes are on the right side with no bony ridge between
them. No species of this type is certainly known from American waters,
although numerous in Europe and Asia. The species have much in common
with the plaice tribe of flounders and may be derived from the same
stock. One species, as above noted, is found in the Miocene.
The common sole of Europe, _Solea solea_, is one of the best of
food-fishes, reaching a length, according to Dr. Gill, of twenty-six
inches and a weight of nine pounds. As usually seen in the markets it
rarely exceeds a pound. It is found from Norway to Italy, and when
properly cooked is very tender and delicate, superior to any of the
flounders. According to Dr. Francis Day, it appears to prefer sandy or
gravelly shores, but is rather uncertain in its migrations, for,
although mostly appearing at certain spots almost at a given time, and
usually decreasing in numbers by degrees, in other seasons they
disappear at once, as suddenly as they arrive. Along the British
seacoast they retire to the deep as frosts set in, revisiting the
shallows about May if the weather is warm, their migrations being
influenced by temperature. The food of the sole is to a considerable
extent molluscous, but it is also said to eat the eggs and fry of other
fishes and sea-urchins.
The spawning season is late in the year and during the spring months.
The ova are in moderate number; a sole of one pound weight has,
according to Buckland, about 134,000 eggs. The newly hatched, according
to Dr. Day, do not appear to be commonly found so far out at sea as some
other species. They enter into shallow water at the edge of the tide and
are very numerous in favorable localities.
As is well known, the sole is one of the most esteemed of European
fishes. In the words of Dr. Day, "the flesh of this fish is white, firm,
and of excellent flavor, those from the deepest waters being generally
preferred. Those on the west coast and to the south are larger, as a
rule, than those towards the north of the British islands. In addition
to its use as food, it is available for another purpose. The skin is
used for fining coffee, being a good substitute for isinglass, and also
as a material for artificial baits.
"The markets are generally supplied by the trawl. The principal English
trawling-ground lies from Dover to Devonshire. They may be taken by
spillers, but are not commonly captured with hooks; it is suggested that
one reason may be that spillers are mostly used by day, whereas the sole
is a night feeder. They are sometimes angled for with the hook, baited
with crabs, worms, or mollusks; the most favorable time for fishing is
at night, after a blow, when the water is thick, while a land breeze
answers better than a sea breeze."
Several smaller species of sole are found in Europe. In Japan _Zebrias
zebra_, black-banded, and _Usinosita japonica_, known as _Usinóshita_,
or cow's tongue, are common. Farther south are numerous species of
_Synaptura_ and other genera peculiar to the Indian and Australian
regions.
=The Tongue-fishes: Cynoglossinæ.=—The tongue-fishes are soles having
the eyes on the left side not separated by a bony ridge, the two being
very small and apparently in the same socket. The body is lanceolate,
covered usually with rough scales, and as often with two or three
lateral lines as with one. The species are mostly Asiatic. _Cynoglossus
robustus_ and other species are found in Japan, and in India are many
others belonging to _Cynoglossus_ and related genera. The larger species
are valued as food. The single European species _Symphurus nigrescens_,
common in the Mediterranean, is too small to have any value. _Symphurus
plagiusa_, the tongue-fish of our coast, is common on our sandy shores
from Cape Hatteras southward. _Symphurus plagusia_, scarcely different,
replaces it in the West Indies. _Symphurus atricandus_ is found in San
Diego Bay, and numerous other species of no economic importance find
their place farther south.
[Illustration:
FIG. 442.—_Symphurus plagiusa_ (L.). Beaufort, N. C.
]