JOURNAL OF THE NEW JERSEY 



E. Fixed moUusks with tliin, pearly, small shells, fixed by the smaller 

 valve which is flat or concave and has a hole or notch at the hinge for 



a plug 2. AnomiidcB. 



E Free mollusks: hinge line straight, formed by ears at the sides of the 



umbo; usually with very distinct radiating ribs 3. Pectiiiidce. 



F, The two muscular impressions very different in size and shape ; generally 

 elongated shells, usually twice as long as high; mussel-shaped, the umbo 

 very near or at the anterior end ; inner layer usually quite pearly ; no 



pallial sinus; hinge Avith st few small teeth or none 4. Mytilidce. 



F. Some Pectens have valves so nearly equal that they might be looked for 



here. (See third E above.) 

 F. Neither mussel nor Pecten shaped. (G.) 



G. Height and length nearly equal ; a decided pallial sinus ; with either 



a plain lunule or else a shell under 8 long 16. Veiieridce 



G. Height and length nearly equal ; no distinct pallial sinus, at the 

 greatest the pallial line is slightly undulated at the posterior end. (J.) 

 G. Length decidedly greater than the height. (H.) 



H. Minute, under 3 long ; no sinus //. Erycinidce. 



H. Pallial sinus distinct ; internal cartilage in deep pits 22. Paphiidce, 



H. Pallial sinus large ; external ligament present, in most cases on the 

 shorter end of the shell ; no internal cartilage. (I.) 

 I. Triangular wedge-shaped, about twice as long as high ; surface with 

 both concentric and radiating strife; our species about 11 long and 



thick for its size ; crenulated within IS. Donacidce. 



I. Length to the height about as 3 to 2 20. Tellinid<v. 



J. With a plain lunule in front of the umbones. (L.) 

 J. With no lunule »nd no ct^noentric ridges. (K.) 



K. With either very distinct radiating ribs or else an almost globular 



shell under 30 long 14. Ccirdiidw. 



K. Shell large, strong, with a thick dark epidermis ; cardinal teeth three 



in each valve 15. Veniliidw. 



Li. Shell with distinct radiating ribs 8. CarditidcF. 



L. Without prominent radiating ribs. (M.) 



M. Over 20 long; compressed, thick, smooth or concentrically furrowed ; 



ligament external; epidermis dark and thick 9. Astartidce. 



M. Shell globular, with strong gonial folds ; ligament in a groove ; no dis- 

 tinct cardinal teeth 12. Ungulinidce. 



M. Shell orbicular, regularly curved, with either laminated concentric 

 ridges or oblique parallel ridges whicli form :ui angle at the centre ; 



