The number of chevrons in the North American and some other specimens is
as follows:
Newport, Rhode Island. 11
Barnegat City, New Jersey. 8(+3?)
Charleston, South Carolina. 8+
Buenos Ayres, Argentina (Burmeister). 11
Holma, Sweden (Malm). 9
Littleton Harbor, New Zealand (Haast). 10
Warrington, New Zealand (Scott and Parker). 9
Pisa Museum (Van Beneden). 9
The chevrons are similar in form in the three North American specimens,
with some differences which will be pointed out below.
_Newport_ (male).—The first chevron consists of a pair of bones which are
not united. They are longer than deep, their depth indeed being less than
that of any one of the succeeding bones except the tenth and eleventh.
Each presents one strong superior articulating facet. Second chevron,
elongated antero-posteriorly, but not much deeper than the first. Third
chevron very deep and only equaled in that respect by the fourth;
narrowed and rounded off below. Fourth chevron largest and broadest
(antero-posteriorly) of the series; expanded below and the lower border
transverse. Fifth to eighth similar in form, but less deep successively,
and the lower border more rounded. Ninth similar to eighth, but smaller
and thinner. Tenth similar to first, longer (antero-posteriorly) than
deep. Eleventh similar to tenth in form, but smaller.
_Barnegat City_ (female).—First chevron bone lacking. Second like that of
Newport skeleton, but smaller. Third similar to second, but much larger
and more produced posteriorly; quite unlike the third in the Newport
skeleton in form, and much less deep. Fourth, largest and deepest of the
series; anterior and posterior borders rounded, and the inferior border
similar. Fifth to eighth similar in form, but successively less deep, and
all more expanded below; inferior border nearly straight. Ninth similar
to eighth, but depth not exceeding breadth; lower angles produced.
_Charleston_ (female, jr.).—The chevrons of this specimen resemble those
of the Newport skeleton, but on account of immaturity they are all more
or less rounded. The two sides of the first chevron are united. The
second is without the posterior angular projection seen in the other
specimens. The third is the deepest of the series. The eighth is not
deeper than long, and hence resembles the tenth chevron of the Newport
skeleton in proportion, but is, of course, much smaller. Two or three
chevrons are lacking from the posterior end of the series.