C(ECUM. 177 



Animal when adult cylindrical : head muzzle-shaped, 

 flanked by cylindrical subulate tentacula bearing minute 

 eyes on (not on bulgings of) their external bases. No 

 lateral cirrhi nor lobes. Foot short, narrow, truncate in 

 front, obtuse behind. No posterior cirrhus. Mantle thick, 

 not fringed. A single branchial plume. Tongue short ; 

 central denticles apparently undeveloped ; two uncini on 

 each side, the inner one broad and serrulated. 



There are few among our British testacea more curious 

 or more puzzling than the singular little shells we have 

 now to describe. Their external aspect seemed so ana- 

 logous to the tooth-shells from which they appeared to 

 differ chiefly in their hinder ends being closed instead 

 of open, that the older conchologists considered them as 

 members of the genus Dentalium. Dr. Fleming first sepa- 

 rated them generically, but with uncertainty respecting 

 their true value or position, since afterwards in his " British 

 Animals" he referred them, unfortunately, to Orthocera. 

 Captain Brown constituted his genus Broclms for them, 

 and Philippi his Odontidium, but Fleming's name of 

 Cwcum has undoubted priority. Mr. Berkeley speculated 

 on their being annelides allied to Ditrupa^ the shell of 

 which, until he discovered its true construction, had been 

 also confounded with Dentalium. Philippi suggested that 

 they might be Pteropoda, a conjecture which need not 

 have been hazarded had our valued correspondent, Mr. 

 Clark, been less indifl:erent to fame, and made known his 

 numerous original researches in good time, since as long ago 

 as 1 834 he had examined and fully ascertained the animal 

 of Caecum trachea^ proving it to be a true mollusk, far 

 removed, however, from Dentalium., though not until 1849 

 were his researches communicated to the public.'"' From 



* Annals of Natural History, 2nd Scr. vol. iv. p. 180. 

 VOL. III. A A 



