NATURAL SCIENCES OP PHILADELPHIA. 15 



Resembles in external form Area pinguis, de Kon., (Anim. Foss., 116, ii. 11). 

 Compare also Cypricardia parvula, {pi. ii. fig. 3). 



The Hamilton group of New York furnishes a fossil similar to the above ; 

 and the Waverly sandstone of Ohio another similar, perhaps identical, one. 



Saxgcinolites (?) jejunus, n. sp. Shell of moderate size, equivalve, trans- 

 verse ; beaks small, barely elevated above the hinge, slightly inflected,. one- 

 third the shell-length from the anterior end; height fully half the length; 

 hinge-line extended ; dorsal slope erect, marked by an internal ridge ; margin 

 slightly inflected, if at all, though some indication exists of a very narrow 

 escutcheon; anterior lunette equally inconspicuous; ventral margin symmetri- 

 cally arcuate between the extremities, with which it connects by similar gradu- 

 ally increasing curvatures; posterior end truncate for a short space near the 

 termination of the hinge-line, with which it forms an angle of about 130 s ; 

 anterior end semi-elliptically rounded. Valves somewhat appressed ; greatest 

 distension one-fourth the distance from the beak to the venter. Surface of 

 cast marked by faint lines of growth. 



Length -86 (100) ; height -48 (55) ; length of anterior end -31 (36) ; of pos- 

 terior - 55 (64) ; thickness of both valves "20 (23). 



Some specimens associated here are relatively shorter posteriorly, but not 

 otherwise distinguishable. 



McCoy's generic names and distinctions, SanyuinolUcs and Leplodomus, 

 seem preferable to King's Allorisma, inasmuch as the latter name, besides being 

 subsequent in time, was originally defined under an erroneous idea, and was 

 finally left to embrace shells regarded as sinupallial, a character which does 

 not seem to belong to the so-called Allorismas of the Palasozoic period. San- 

 guinolites lowensis, and probably some of the others just described, are allied in 

 form to Cypricardia ; but I agree with Pictet and others in believing that, 

 while we have no evidence of the existence of the teeth of Cypricardia in any 

 of the Palaeozoic species generally referred to that genus, it is more natural to 

 throw them into another association. Moreover, the sharply-inflected dorsal 

 margin and broad, elongate posterior escutcheon, present in all the species of 

 Ccelonotidie, would seem to indicate real affinities, and thus withdraw the 

 Allorisma type entirely from the association in which it has been placed. 

 Cypricardia? riyida, White and Whitfield, from the same rocks, is &Sanyui?io'<U < '. 



CARDIOMORPHA, de Koninck. 



Cardiomorpha trigonalis, n. sp. Shell small or of moderate size, triangular, 

 rather ventricose, with elevated, incurved beaks. Ventral margin slightly con- 

 vex anteriorly, slightly sinuate near the posterior angle ; anterior angle regu- 

 larly rounded to the subtruncate anterior side ; posterior angle rather acute,' 

 formed by the termination of the sharp postumbonal ridge, from which the 

 surface descends precipitously to the truncate posterior margin. Hinge- line 

 short, rounded, edentulous. Greatest thickness a little above the middle of the 

 shell. Surface marked only by faint incremental stria?; younger specimens 

 smooth. 



Length -82 (100) ; height -72 (88); thickness of both valves -50 (61). 



This species has been sometimes regarded as C. rhomboidea, Hall, but none 

 of the numerous specimens of it exhibit the least trace of radiating lines. 

 The outline, moreover, is subtriangular instead of subrhomboidal. (Compare 

 with C? trianyulata, Swallow, St. Louis Trans., i. 655.) 



ARCA, Linnaeus. 



Arca modesta, n. sp. Shell small, very ventricose, quadrate-oval, with a 

 posterior alate prolongation of the hinge-line. Beaks subterminal, incurved, 

 separated by a ligamental area; posterior hinge-line straight, nearly as long 

 as the shell. Umbonal ridge and body of the shell inflated to the ventral mar- 



1863.] 



