234 ASTARTID^. 



Carditopsis, E. a. Smith, 1881. 



Distr. — G.flahellum^ Reeve. 



Shell without external ligament ; cardinal teeth one on one 

 side of the cartilage-pit, and two united above on the other side ; 

 lateral teeth more delicate than in Carditella, internal ligament 

 considerably larger. 



Pleurophorus, King, 1848. 



Syn. — IJnionites, Wissm. 



Diatr. — P. costatus, Brown (cxxi, 6). Permian; England. 



Shell oblong ; dorsal area defined by a line, or keel ; umbones 

 anterior, depressed; hinge-teeth 2-2; laterals I'l, elongated, 

 posterior; anterior adductor impression deep, with a small pedal 

 scar close to it, and bounded posteriorly by a strong rib from the 

 hinge ; pallial line simple. 



Matheria, Billings, J 858. 



Etym. — Dedicated to Mr. Mather, of the Geological Survey of 

 New York. 



DLstr. — M. tenera^ Billings (cxxii, 57-59). Trenton limestone ; 

 Canada. 



Shell transverse, equi valve ; beaks near the anterior end ; two 

 small obtuse cardinal teeth in the left valve, and one in the 

 right ; ligament external. 



Septocardia, Hall and Whitfield. 



Distr. — S.typica. Jurassic; Nevada. /S. rara. Meek (cxxii, 

 55, 56 . 



Shell inequilateral, cordiform ; hinge strong ; right valve with 

 a strong, recurving, hooked tooth under the beak, and a deep 

 cavity below and exterior to it, which is profoundly excavated 

 in the thickened substance of the shell ; in the left valve a large 

 deep cavity corresponds to the tooth of the right valve ; lateral 

 teeth obsolete ; ligament external, situated in a groove formed 

 by a thickened, overlapping portion of the shell posterior to 

 the tooth and corresponding cavity ; anterior adductor muscular 

 scar very large and deep, separated from the general cavity of 

 the shell by a calcareous plate, or septum, extending across the 

 anterior end of the valve on the inner side of the scar, thereby 

 forming a distinct chamber in each valve ; posterior adductor 

 scar much smaller, situated within the posterior cardinal margin ; 

 pedal scars not observed ; surface of the shell marked in the 

 typical species by strong, elevated, radiating ribs, with orna- 

 mfented surfaces similar to many of the recent species of Cardium. 



Anodontopsis, M'Coy, 1851. 

 Distr. — Silur.; Eng., U. S. Type, A. angustifrons, M'Coy. 



