346 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



posteriorly ; teeth as iu Amiantis, but left posterior cardinal deeply 

 grooved ; nymphs longitudinally ribbed ; palliul sinus linguilbrm, 

 rounded, or obtusely angular. 



This section corresponds with the Bione group of Romer, but must, 

 I think, also include one species which has been referred to Pitaria, 

 viz. the Cytherea cor oi Hauley. 



Section Agriopoma, Dall, 1902. Type, Cyth. Texasiana, Dall. 



Outer surface dull and chalky ; nymphs smooth, median and 

 anterior cardinals of right valve forming a complete arch ; left 

 posterior long and partly free, left median narrow. Pallial sinus 

 sharply angular. 



Genus Pitaria, Homer, 1857, em. 



Synonyms: Caryatis, Homer, 1862; Dione, Gray (in part). 



Shell oval or sub-trigonal, smooth or finely striate ; lunule super- 

 ficial ; escutcheon not defined ; ligament short and deeply sunk ; 

 teeth in left valve like those of Amiantis, but posterior cardinal 

 generally more or less separate from the nymph ; in the right valve 

 the anterior and posterior cardinals are often united to form an arch 

 over the median ; pallial sinus generally short and rounded, often 

 ascending. 



Pitaria (s.s.). Type, Venus tumens, Gmelin. 



Nymphs longitudinally ridged ; left posterior cardinal long and 

 confluent; left median triangular ; right cardinals separate ; pallial 

 sinus deep and pointed. This small group is a link with Amiantis. 



Section Calpitaria, J. -Br., 1908. Type, Cytherea sulcataria, Lara. 



Left posterior cardinal partly free and oblique ; median triangular ; 

 right cardinals separate ; pallial sinus short and rounded. 



Section Pitarina, nov. sect. Type, C. citrina, Lam. 



Nymphs smooth ; left posterior cardinal free and crossing the 

 hinge-plate obliquely ; pallial sinus short, rounded, ascending ; two 

 outer cardinals of right valve forming a complete arch. 



Siih-gmera. 



Callizona, n.subgen. Type, Callista vulnerata, Brod. 



Shell thick, sub-orbicular, glossy ; valve - margins irregularly 

 crenulated; nymphs smooth; hinge strong; left posterior cardinal 

 long and partly free as in Calpitaria ; right posterior cardinal short 

 and entire, rugose ; pallial sinus short and rounded. Only the one 

 species known. 



Callocardia, A. Adams. Type, C. guttata, A. Adams. 



Shell very thin ; hinge-plate narrow and excavated between the 

 teeth ; the united cardinals in each valve forming complete arches 

 which are regularly curved and not angular; left posterior tooth long 

 and free, but parallel to nymph ; right posterior cardinal formed of 

 two plates, one of which is continuous with the anterior tooth ; 

 pallial line obscure, but believed to be entire. 



Leucothea, n.subgen. Type, Callocardia Birtsi, Preston. 



Shell very thin, dull white, concentrically striated; hinge-plate 

 short, deeply excavated, and narrowed posteriorly ; nymphs narrow, 



