646 



ARTHROPODA 



SUB-KINGDOM VII 



perhaps certain Carboniferous species. Fossil remains are extraordinarily profuse in 

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



Palaeocypris, Brongt. Shell 0'5 mm. long, sub-ovate, smaller posteriorly than in 

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



Mtiller (Fig. 1346). Shell reniform or oval, thin, translucent, smooth or 

 hirsute, often punctate; hinge edentulous, somewhat 

 thickened; ventral margin often sinuate. Tertiary to 

 Eecent. 

 c Cypridea, Bosq. (Fig. 1347). Like Cypris, but with 



FIG. 1346. 



Cypris faba, Desm. Miocene; 

 Oeningen, Switzerland. A, Side, and 



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



C, Valves composing fresh -water 

 limestone at Nb'rdlingen. 



FIG. 1347. 



Cypridea Waldensis, 

 Sowb. Wealden ; Ober- 

 kirchen, Hanover. l*/j. 



FIG. 1348. 



Bairdia curta, M'Coy. 

 Carboniferous Limestone ; 

 Ireland. 15/ X (after 

 Kirkby). 



small hook-like projection at the antero- ventral angle. Purbeck and Wealden. 



Bairdia, M'Coy (Fig. 1348). 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 overlap- 

 ping edge of left valve. Ordoviciaii 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 Palaeozoic forms have also been assigned to this genus. 



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

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

 Jurassic to Recent. 



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

 simple without overlap. Silurian, Carboniferous, Pleistocene, and Recent. 



Family 6. Cytherellidae. Sars. 



Family characters chiefly zoological. Shell minute, inequivalve, thick, calcareous, not 

 notched anteriorly. 



Cytherella, Jones (Fig. 1349). Shell oblong or sub-ovate, compressed in front; 

 surface generally smooth, but sometimes undulating and marked 

 with pits and granules. Contact margin of the larger right valve 

 grooved for reception of flange -like edge of smaller left valve. 

 Ordovician to Recent. 



Cytherellina, Jones and Holl. Silurian. ? Pachydomella, 

 Ulrich. Devonian. Bosquetia, Brady. Recent. 



Family 7. Entomidae. FIG. 1349. 



Cytherella cmnpressa, 



Shells relatively short, strongly convex, reniform, ovate or rounded Munst. sp. oiigocene ; 

 quadrate, sub-equivalve, with a more or less well-marked depression near 22/j p (afterBosquetf mi 

 the middle of dorsal region. Surface sculpture concentric or radiate. 



Entomis, Jones (Figs. 1350, 1351). Shell sub-ovate or fabiform ; valves with a 

 slightly curved sub-median vertical furrow extending to hinge line ; in front of furrow 

 occasionally a rounded tubercle. Surface marked generally with raised, concentric, 



