PALJEONTOLOGY OF NEW YORK. 



the ;iiitcri>-latcr;il inai-iii with littk' variation. Beaks obtuse, nmiHU'd, 

 anterior to tlic mi. Idle ol' the liin<;e. rnil>o sul)ten(lin<r an anj,de of 

 ahout l;5(r. 



Kars hiiL'f, triaiiiiiilar: |iosterior onr the hirj^er, and definc(l hy tlie abrupt 

 slojic of the side of the niiil.o. wliih" tiie anterior ear is separated l>_v a 

 ilislinct suhais ; lateral niarLiins concave, beconiin<i convex at tlir hinge- 

 line Hvssal-sinus broad, rounded, well-delincil and iiidirntcil on the ear 

 1)\ a snlcus extendinir to the cxti'einity of the beak. 



The rifiiit valve is flatter and [)roportionuliy broader than the lelt. The 

 limits of the ears are clearly indicated by the rapid slope of the nmlio, and 

 the al)sence of strong radiating lines of ornamentation. 



Test thin, marked iiy numerous regulai- alternating rays, which increase 

 in numlier li\ interstitial additions, and become broader and stronger towards 

 the margins. These radiating ribs are crossed by very fine, sharp stria? of 

 growth. < In tlie ears the rays are neai'ly obsolete, and the lines of growth 

 are sharper and stronger than on tlie body of the shell. 



The internal mould ])reserves, in a sn])dued degree, the ornaments of 

 the exterior, and shows a simiile, continuous pallial impression, extending 

 nearly parallel to the margins, ami terminating in a large sub-ovate muscular 

 impression, which is posterior tt) the middle of the shell. The eavit}' 

 beneath the beak extends over the ligameutal area at that jjoint, forming 

 the cartilage-pit. In young individuals the ligameutal area shows three or 

 foui' small furrows at the heak, extending towards the extremities of the 

 hinge-line. Three of these furrows measure - mm. across. In larger and 

 older individuals, this furrowe(l ligameutal area is nuich more marked, 

 having frequently a width of ■") mm., and extends the entire length of the 

 hinge, showing more numerous furrows. At the beaks the furrows are bent 

 slightly outwards, otherwise, with gentle undulations, they run parallel to 

 the hinge line. This feature is a constant character in this and several 

 other .species, and is similar to that in many forms of Pterinea and 

 Lykiopecten. 



The diminsions of the shells of this species are very variable. Large 



