86 PLEIOCENE FOSSILS. 



This fine species is easily distinguished from its congeners, so well represented in our 

 newer Tertiary formations. The prominent folds, radiating from the beaks to the pallial 

 margin, separate it from every other species of the genus. In other respects it is subject 

 to variation, in some specimens the folds extend quite to the beaks, and in others, they 

 do not commence till after the shell has attained an inch or two in height. The shell is 

 often inflated and ponderous, whilst in other forms it is more or less compressed, with the 

 anal side prolonged, resembling in outline V. Rileyi. The radiating folds are also subject 

 to variation in form and position. In some varieties, the folds -are few and prominent, 

 terminating at the margin in deep notches, which suggested the specific name tridac- 

 noides, whilst in others the folds are reduced to mere undulations, which extend over the 

 entire shell. 



We have a specimen of V. permagna, Con., before us, in which a similar fold extends 

 across the shell. 



V. tridacnoides, though rare in South-Carolina, is quite abundant in the Meiocene 

 beds of Virginia. 



Plate XXII. Fig. 1, Natural size. 



Locality. Darlington District. 



Museum, College of Charleston. 



VENUS P E E M A G N A. ( ? ) — C o n. 



Plate XXII. Fig. 2. 



Venus permagna, Con., (obs. on V. Mortoni,) Foss. Ter. For., p. 8. 



V. testa ovata, cordata, sub-inflata, concentrice rugoso-striata, latere email sub-pltcato, 

 arcuato; margine palliali crassi, Icevi; lunula impressa, oblongo-cordato. 



Description. Shell thick, ovate, cordate, somewhat inflated, concentrically and roughly 

 striate; anal side, with obsolete folds, arcuated; pallial margin thick, smooth, lunule 

 impressed, oblong-cordate. 



