The members of this class are rather primitive and have a long geologic
history. These brachiopods have valves which are not provided with hinge
teeth, the valves being held together by muscles, and a hinge-line is
lacking (fig. 14). Most inarticulate brachiopods are circular or
tongue-like in shape and commonly composed of chitinous and phosphatic
material. Inarticulate brachiopods range from Lower Cambrian to Recent
in age but were never as common as the articulate brachiopods, which are
described below. Brachiopods belonging to this class have been recorded
from several Paleozoic formations in Texas (Pl. 17, _Lingula_,
_Apsotreta_, _Angulotreta_).
[Illustration: Plate 17]
[Illustration: PENNSYLVANIAN BRYOZOANS]
FISTULIPORA × 6
POLYPORA × 5
RHOMBOPORA × 8
[Illustration: CAMBRIAN BRACHIOPODS]
APSOTRETA × 10
LINGULA × 4
ANGULOTRETA × 10
[Illustration: MISSISSIPPIAN BRACHIOPODS]
RHIPODOMELLA × 1
DICTYOCLOSTUS × 1
CAMAROTOECHIA × 1
[Illustration: Fig. 14. _Lingula_, a typical Recent inarticulate
brachiopod showing extended pedicle.]
Pedicle
Valve