230 ASTARTIDA. 
Opts, Defrance. 
Etym.—Opis, a name of Artemis. 
Distr.—Fossil, 42 sp. Trias—Chalk; Europe. 0. lunulata, 
Miller (exxi, 33). 
Shell strong, ventricose, cordiform, obliquely keeled; beaks 
prominent, incurved, or subspiral; cardinal teeth 1:1; lunule 
distinct. 
opisoMA, Stoliczka, 1870. Shell trigonal, much higher than 
long, with long attenuated slightly incurved and approached 
beaks, lunule large and deep; hinge with three elongated cardinal 
teeth in each valve, and a small posterior lateral tooth situated 
above the posterior muscular impression, which is only slightly 
larger than the anterior one, both being deeply excavated. 
Species referable to this group occur in Upper Jurassic and 
Cretaceous rocks; in form they perfectly resemble some species 
of Opis, but the hinge is considerably different, possessing 
more cardinal teeth than are to be observed in that genus. O. 
Geinitziana, Stol. (cxxii, 38). 
Prosocatus, Keferstein, 1857. 
Distr.—3 sp. Devonian; Eur. P. ovalis, Keferstein (cxxii, 
45, 46). 
Shell long oval, thick, smooth, lunule deep; cardinal teeth 2°2, 
the anterior oblique, the posterior strong and lengthened, nearly 
parallel with the hinge-margin; no lateral teeth; anterior mus- 
cular impression deep, posterior shallow. 
Pacuypbomus, Morris, 1845. 
Etym.—Pachus, thick ; domos, house. 
Syn.—Megadesmus, Sowb. 
Distr.—Fossil,5sp. Devonian? New South Wales, Tasmania. 
Shell oval, ventricose, very thick; ligament large, external ; 
lunette more or less distinct; hinge-line sunk; teeth one or two(?) 
in each valve; adductor impressions deep; anterior pedal scar 
distinct ; pallial line broad and simple, or with a very shallow 
sinus. 
notomyA, M’Coy, 1847. (Mzonia, Myonia, Pyramia, Cleobis, 
Dana.) Shell transversely oval, subequivalve, inequilateral, 
solid, slightly gaping at both ends; hinge with one strong tooth 
in the right valve, which appears to correspond to a pit in the 
left, the two muscular impressions are large and deep, a third, 
small accessory one is situated above the anterior large one; 
pallial sinus very small, or only indicated by a truncation of the 
pallial line; ligament strong, external. Paleozoic; New South 
Wales. P. securiformis, M’Coy (exxi, 10). 
ASTARTILA, Dana, 1849. Shell elongately subtriangular, inequi- 
lateral, slightly inflated, moderately thick at the beaks and near 
