56 ' Bulletin 5 336 



150 FOSSIL SHELLS. 



becoming obsolete behind the cavity of the umbo ; 

 on the opposite valve is an impressed line, occu- 

 pying a similar position. Whether or not this line 

 is characteristic, I am unable to determine, having 

 seen but two valves. 



C. concentrica. Born. Mr. Finch's differ from 

 those now existing on our southern coast, in being 

 larger. 



Length three inches and three-tenths, breadth 

 three inches and two-fifths. 



ASTARTE, Sowerby. 



I. A. undulata. PI. ix. fig. 5. Shell trigonate, 

 umbones flattened, and with profound undulations ; 

 apices very acute. 



Description. Basal half of the shell coarsely 

 wrinkled, the remaining half deeply, regularly and 

 widely undulated on the flattened umbo : hmule 

 large oblong subovate, concave, separated from 

 the disk, particularly near the beaks, by an acute 

 angle : beaks prominent, approximate, acute, turn- 

 ed a little backward at tip : ligament margiii con- 

 cave nearly to the basal angle, and separated from 

 the disk, near the beaks, by an acute angle : liga- 

 ment very short : teeth regularly crenated each 

 side : basal angles rounded : basal edge nearly 

 rectilinear, or very obtusely arcuated ; within finely 

 crenated ; smaller muscular impression very dis- 

 tinct. 



[J. A. N. S., Phila., ist Ser., Vol. IV, 1824.] 



