740 



ARTHROPODA 



PHYLUM VII 



Family 5. Cypridae Zenker. 



Minute, mostly reniform or elongate-ovate, corneous or corneo-calcareous shells, ivith 

 thin, someivhat unequcd valves, one overlapping the other either ventrally or dorsally or 

 both. 



Recent Cypridae are chiefly fresh-water inhabitants, but this is true in a lesser 

 degree of the fossil forms. All the Paleozoic representatives are marine, excepting 

 perhaps certain Carboniferous species. Fossil remains are extraordinarily profuse in 

 certain deposits, and the family is an important rock-builder. 



Palaeocijpris Brongt. Shell 0*5 mm. long, sub-ovate, smaller posteriorly than in 

 front ; surface granulose and finely hirsute in dorsal region. Carboniferous. 



Gypris Miiller (Fig. 1428). Shell reniform or oval, thin, translucent, smooth or 

 A hirsute, often j^^mctate ; hinge edentulous, somewhat 



thickened ; ventral margin often sinuate. Tertiary to 

 Recent. 



Fig. 1428. 



Cyi->ris faba Desm. Miocene; 

 Oeningen, Switzerland. A, Dorsal, and 



B, Lateral view, is/j (after Bosquet). 



C, Valves composing fresh-water lime- 

 stone at Nordlingen. 



Fig. 1429. 



Cypridea waldensis 

 Sowb. Wealden ; Ober- 

 Isirchen, Hanover. 15/^. 



Fig. 1430. 



Bn.inlia curta M'Coy. 

 Ijow er Carboniferous ; 

 Ireland. 15/j (after 

 Kirkby). 



Cypridea Bosq. (Fig. 1429). Like Gypris, but with a small hook-like projection 

 at the antero-ventral angle. Purbeck and Wealden. 



Bairdia M'Coy (Fig. 1430). Shell sub- triangular or rhomboidal, with the 

 greatest height near the middle, generally smooth, both extremities narrowly rounded 

 or pointed. Dorsal margin more or less strongly convex ; hinge formed by over- 

 lapping edge of left valve. Ordovician to Recent ; maximum in Carboniferous. 



Bythocypris Brady. Shell smooth, reniform, ovate or elliptical ; left valve over- 

 lapping the smaller right valve usually on both dorsal and ventral margins. 

 Typically Recent, but a number of Paleozoic forms have also been assigned to this 

 genus. 



Macrocypris Brady. Similar to the last, but generally more elongate, posteriorly 

 more acuminate, and the right valve larger than the left. Ordovician and Silurian ; 

 also Jurassic to Recent. 



Pontocypris Sars. Like Bythocypris, except that the shell is very delicate, and 

 the hinge is simple without overlap. Silurian, Carboniferous, Pleistocene and Recent. 



Fig. 1431. 



Cytherclla conipressa 

 (Miinst.). Oligocene ; 

 Riippelmonde, Belgium. 

 22/i (after Bosquet). 



Family 6. Oytherellidae Sars. 



Family characters chiefly displayed by soft parts. Shell minute, 

 incquivalve, thicJc, calcareous, not notched anteriorly. 



Gytherella Jones (Fig. 1431). Shell oblong or sub -ovate, 

 compressed in front ; surface generally smooth, but sometimes 

 undulating and marked Avith pits and granules. Contact margin 

 of the larger right valve grooved for reception of flange -like 

 edge of smaller left valve. Ordovician to Recent. 



Gytherellina Jones and Holl. Silurian. (?) Pachydomella 

 Ulrich (Fig. 1426, d) ; Bosquetia Brady. Recent. 



