20 

 Cabinet of the Acad. Nat. Sciences, No. 820. 



OBSERVATIONS. 



This shell is represented in Turton's figure with 

 the basal margin straight, as we find it in youth and 

 middle age, and it is only when old that it becomes 

 arcuated: it is thin, translucent, bluish white, and 

 covered with an olivaceous epidermis; a reddish 

 brown stripe passes from the apex towards the oppo- 

 site margin, and marks the course of the internal rib; 

 from this character Turton has given it the specific 

 name of tseniata, as its original appellation is pre- 

 occupied in the genus Psam?nobiay to which he has 

 referred it. It has a single tooth in one valve, and 

 two very dissimilar teeth in the other, the largest 

 being curved and flattened at the top. 



Maton and Racket have adopted the opinion of 

 Montagu, that this shell is the S. antiquatus in its 

 incomplete state, but the specimen here figured has 

 every appearance of maturity, and certainly bears no 

 resemblance to S. antiquatus^ as figured in Pennant's 

 British Zoology, nor has that species been discovered 

 upon our coast. 



I am indebted lo Mr. D. B. Smith for the use of 

 a very perfect shell of this species, found on the coast 

 of Rhode Island by Lieut. Brown. Col. Totten, of 

 Newport, has since politely sent for my inspection 

 the largest and most beautiful specimens I have seen ; 

 in one of these the epidermis is obscurely radiated, 

 beneath which the shell is pale violaceous. They 

 are from the vicinity of Newport, where, as Col. 



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