CONCH YLI A—DITHYRA. 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, gradually dilating 

 itself outwards in diameter. 



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

 the segments of vrhlch are united by thin elastic membranes. The 

 back has two 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 lio-ament. 



This rare and very singular species appears to have been known 

 to Solander, and the late dutchess 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 Dutchess, from which he had draw- 

 ings made by Agnew, her Grace's gardener. And there appears 

 very little doubt but that it is the species alluded to in the manu- 

 scripts of Solander, and from these manuscripts quoted in the 

 Portland Catalogue. Mr. Humphrey jmrchased the lot. 



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

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



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