246 NEW FOSSIL SHELLS 



This shell may be distinguished from all its congeners of our Tertiary by its small 

 and numerous costae, and longitudinal form. 



P. TENUIS, PL. 35. FIG. 33. 



P. testa sub-orbicular 'i, aquilaterali, convexd, lenuf, striatd; striis radiantibus, crebris, turn magnis, turn parvis 

 lineis concentricis, minutis, raris; natibus acuminatis, sub-elevatis; auribus magnis, ineequalibus, striatis; testa in- 

 terne Icevi. 



Shell sub-orbicular, equilateral, convex, thin, striate; striae radiating, numerous, sometimes large, sometimes small; 

 a lew minute concentric lines; beaks acuminated, somewhat elevated, auricles large, unequal, striate; shell smooth 

 within. 



Diam. .60. Length 2.26. Breadth 2.28 inches. 



Remarks. The strise are very irregular as to size, and frequently are alternate. Near 

 the base they are much smaller; and are decussated by numerous very minute, concen- 

 tric lines. On the only valve now before me, they are about one hundred in number. 

 The shell has been quite longitudinal when young, as may be seen from the lines of 

 growth. Three or four of the longitudinal strise are rather. larger than the rest, particu- 

 larly near the beaks. 



This pretty shell was found at Shell Bank near Petersburg, the plantation of E. 

 Ruffin, Esq., and sent by him to my father. It may be distinguished from P. Clinto- 

 nius, Say, a species to which it is closely allied, by its unequal auricles and strice, its 

 more longitudinal form, and acuminate beaks. 



GENUS PLICATULA. 

 P. RUDIS, PL. 35. FIG. 34. 



P. testa longilud/nali, orbieulari, pland, tenui, rugosd; natibus prominulis, acutis; dentibus magnis; margine intus 

 lato, nigrescente. 



Shell longitudinal, orbicular, flat, thin, rugose; beaks prominent, acute; teeth large, internal margin wide and 

 blackish. 



Diam .20. Length .68. Breadth .65 of an inch. 



Remarks. The surface is nearly covered with irregular longitudinal wrinkles, which 

 render it very rugose. It is nearly flat and destitute of folds. 



This shell may be distinguished from the P. marginata, Say, which it somewhat 

 resembles, by its flat, orbicular form, rugosities, thinness and want of folds. It is much 

 rarer than that species. I found but three or four specimens of it among more than a 

 hundred of the other. 



FAMILY PHYLLIDID^:. 



GENUS CHITON. 



C. TR4NSENNA, PL. 35. FlG. 35. 



C. testa , octovalvi? crassd, costatd, dorso valdc elevatd et angulata; valvarum intermediarum area centrali costis 

 longitudinalibus rectis, noduliferis, area lateral! aut Icevi out nodulosd; valvce terminalis area centrali noduloso 

 costatd, area laterali nodulosd. 



