PLEIOCENE FOSSILS. 73 



CRASSATELLA.— Lam. 



CRASSATELLA UNDUE AT A. — Say. 



Plate XX. Figs. 5 to 8. 



Crassatella undulata, Say, Jour. Ac. Nat. Sci., Vol. 4, p. 142, pi. 11, fig. 2. 

 Crassatella undulata, Con., Foss. Shells, Ter. For., p. 23, pi. 9, fig. 1. 

 Crassatella undulata, Con., Foss. Ter. For., p. 21, pi. 9, fig. 2. 



C. testa sub-trigona, crassa, incequilateralis; umbonibus sulcatis, depressis; latere buccali 

 brevi; latere anali elongato, producto, oblique truncato; lunula lanceolata, excavata. 



Description. Shell somewhat triangular, thick, inequilateral; umbones sulcate, flat- 

 tened; buccal side short; anal side elongately produced, obliquely truncated; lunule 

 lanceolate, excavated. 



This fine species is subject to great variation in the form of the shell. In one variety, 

 which is the most common, the anal side is greatly produced, making the shell very 

 inequilateral ; this prolongation takes place only after the shell has attained to a certain 

 size. In another variety, the shell is nearly equilateral, and between these extremes, 

 intermediate forms are found. In the young of all, however, the flat, sulcate, umbonal 

 parts are always preserved. 



Compare the young of both species as figured in plate XX, figs. 7 and 10. 



Plate XX. Fig. 5, Interior of right valve. 



" 6, Exterior of right valve. 



" 7, Young shell. 



" 8, Variety. 



Locality. Sumter District. 



Museum, College of Charleston. 



