576 Forty-fifth Report on the State Museum. 



Type, Schizomania Jilosa, Hall. 



Distribution. Lower Silurian to (?) Devonian. The genus is 

 American and the typical species are found in the fauna of the 

 Hudson River group. 



Crania, Retzius. 1781. 



a (Plate 6, Figs. 14-23,) 



Synonyms. Numulus, Stoboeus, 1732 ; Waller, 1778 ; Anomia, 

 Linne, 1760; Ostracites, Beuth, 1776; Patella, Muller, 1776; 

 Criojpus, Or iopoderma, Poli, 1791, 1795; Orbicula, Cuvier, 1798; 

 Lamarck. 1799 ; Orbicularius, Dumeril, 1806 ; Oraniolites, Schlo- 

 theim, 1820 ; Choniopora, Schauroth, 1854. 



Shell inequivalve, inarticulated, Avithout perforation for a 

 pedicle ; sub 4 circular in outline, generally somewhat transverse 

 across the posterior margin ; attached by the apex or the 

 entire surface of the lower valve. Ventral or lower valve 

 depressed -conical or conforming to the surface to which it is 

 attached. Dorsal or upper valve more or less conical with a sub- 

 central, posteriorly directed apex. External surface of the 

 valves usually smooth, sometimes spinose or with concentric or 

 radiating striae. In the interior of both valves are two pairs of 

 large adductor scars, the posterior of which are close upon the 

 margin and widely separated, the anterior near the center of the 

 shell and close together, more approximate in the lower than in 

 the upper valve. These posterior scars are often strongly ele- 

 vated on a central callosity which surrounds their broad and 

 thickened margins. Impressions of the pallial genital canals 

 anterior. The margin of the lower valve is usually coarsely 

 digitate. 



Shell-substance calcareous; strongly punctated by vertical 

 canals which become subdivided toward the epiderma lsurface. 



Animal provided with two spiral arms, whose apices are 

 directed toward the dorsal valve. The alimentary canal forms a 

 convolution on the right side, the anus opening near the center 

 of the ventral valve. Liver large; genital glands six in number, 

 two in each mantle lobe and two in the visceral cavity. Mantle 

 without marginal seta 1 . 



128 



