CONCUR LI a— BITHTR A. 1. 



rather oblique crenate ribs: near the middle is a somewhat oblique 

 longitudinal groove, beyond which it is striate in a coarser 

 manner and more straight direction: the smaller end is open, 

 truncate, and invested with a very thin ring, which extends more 

 than a quarter of an inch beyond the truncated termination, gradu- 

 ally dilating itself outwards in diameter. 



This ring, or circular appendage, is divisible into two equal 

 parts, the segments of which are united by thin elastic mem- 

 branes. The back has two small accessorial appendages, with 

 the edges of the valves reflected at the anterior end, so as to 

 form a kind of double obtuse keel which reaches as far as the 

 longitudinal groove, near the end of which is a kind of raised 

 joint, where the accessorial valves are fixed: inside dull white, 

 with a longitudinal rib corresponding with the outside groove : 

 teeth rather short, flat, and on the margin, above the teeth, is an 

 erect somewhat triangular and rather concave plate, which in one 

 of the valves is much larger, and contains a portion of the animal 

 fold, but no distinct permanent ligament. 



This rare and very singular species appears to have been 

 known to Solander, and the late Duchess of Portland, Mr. 

 Swainson, of Elm- Grove, near Liverpool, who has lately obtained 

 some specimens from Torbay, informs us, that he is in possession 

 of a very small pair, presented to him by the Duchess, from which 

 he had drawings made by Agnew, her Grace's gardener. And 

 there appears very little doubt but that it is the species alluded to 

 in the manuscripts of Solander, and from these manuscripts quoted 

 in the Portland Catalogue. Mr. Humphrey purchased the lot. 



A single specimen was found on the strand near Exmouth, by 

 Mr. Loscorabe. And it has since been discovered to inhabit the 



B 2 



