934 ASTARTIDA, 
CarpirTopsis, EK. A. Smith, 1881. 
Distr.—C. flabellum, 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. 
PLEvuROPHORUS, King, 1848. 
Syn.—Unionites, Wissm. 
Distr.—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 1-1, elongated, 
posterior; anterior adductor impression deep, with a small pedal 
sear close to it, and bounded posteriorly by a strong rib from the 
hinge; pallial line simple. 
MatuertA, Billings, 1858. 
Etym.— Dedicated to Mr. Mather, of the Geological Survey of 
New York. 
Distr.—M. tenera, Billings (cxxii, 57-59). Trenton limestone ; 
Canada. 
Shell transverse, equivalve; beaks near the anterior end; two 
small obtuse cardinal teeth in the left valve, and one in the 
right; ligament external. 
SeprocarpiA, Hall and Whitfield. 
Distr.—S. typica. Jurassic; Nevada. S. rara, Meek (cxxii, 
5d, 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 
sear 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- 
mented surfaces similar to many of the recent species of Cardium. 
Awnopontopsis, M’Coy, 1851. 
Distr.—Silur.; Eng., U. 8. Type, A. angustifrons, M’Coy- 
