512 



In many inftances, however, the ridge along the back 

 is fo nearly obfolete, efpecially in old (liells, and fuch as 

 are grouped, that they would with difficulty be fepa- 

 rated from S. vermicidaris, were it not for the animal ; 

 fuch have been generally confounded for that fpecies, 

 and is figured by Ellis ; but the fingle, trumpet-ihaped 

 probofcis, of the animal, forbids it to be the J?, vcr- 

 viicularis. 



That figured by Donovan, appears alfo to be a tri- 

 quetra for the fame reafon, but the tentacula of the ani- 

 mal are wanting in this figure; though that part is very 

 well reprefented by Ellis. 



It is with no fmall difficulty, and in fome degree un- 

 certainty, that we have placed the fynonyms to this and 

 the preceding fpecies, as heretofore the animals have not 

 been attended to fufficiently, to form the bed and fureft 

 charafter of diftinftion. 



If the triquetra, and the Linncean contortuplicata be 

 careful I V examined, the animals will be found to be the 

 fame, pofTeffing onlv a lingle, trumpet-fliapcd probofcis, 

 as reprefented by Ellis for \.\\e Ve.rmicularis : and it 

 will be obferved, that all the fhells inhabited by fuch 

 animal, are, whether grouped or fingle, more or lefs 

 furnifhed with a dorfal rids[e, thongrh in fome of the lar- 

 gerfpecimensit isfcarcely tohedircerned, orat leaf! might 

 be paffed unnoticed. On the contrary, the vermicularis 



and 



