230 ASTARTID.E. 



Opis, Defrance. 



Etym. — Opis, a name of Artemis. 



Bistr. — Fossil, 42 sp. Trias — Chalk; Europe. 0. lunulata. 

 Miller (cxxi, 33). 



Shell strong, veutricose, cordiform, obliquely keeled ; beaks 

 prominent, incurved, or subspiral ; cardinal teeth I'l ; lunule 

 distinct. 



OPISOMA, Stoliczka, 1810. 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). 



Prosoc(Elus, Keferstein, 1851. 

 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. 



Pachydomus, Morris, 1845. 



Etym. — Pachas, thick ; domos, house. 



Syn. — Megadesmus, Sowb. 



Distr. — Fossil, 5 sp. 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, 1841. (Mseonia, Myonia, Pyramia, Cleobis, 

 Dana.) Shell transversely oval, subequivalve, inequilateral, 

 solid, slightly gaping at both ends; hinge with one strong tooth 

 in the I'ight 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. Palaeozoic ; New South 

 Wales. P. securiformis, M'Coy (cxxi, 10). 



ASTARTiLA, Dana, 1849. Shell elongately subtriangular, inequi- 

 lateral, slightly inflated, moderately thick at the beaks and near 



