180 Mr. W. Clark on Csecum trachea and C. glabrum. 



XX. — On the Animals of Csecum trachea and C. glabrum. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History, 



GENTLEMEN, Norfolk Crescent, Bath, June 28th, 1849. 



In the year 1834 I discovered the animal of Ccecum trachea, in 

 the coralline zones off Exmouth ; notes were then made on it, 

 but only communicated to a few friends, and I am not aware that 

 any author has mentioned the animal since that time, except in 

 doubt, as to its character and position. Having within the last 

 week, at the same place, examined many of this curious and 

 minute species, I am enabled to give a particular description 

 thereof, as well as some account of the still more minute conge- 

 neric species, Caecum glabrum, now seen for the first time. 



The shells of these animals have, from their forms, long been 

 located with the Dentalia, but it will appear that in respect of 

 the animal they have little connection with them ; they have also 

 had other places assigned to them, and malacologists are still in 

 doubt with regard to their natural position. I therefore think 

 this account may interest some of your readers, and assist to 

 determine the proper " locus standi a of these mollusca. 



CiECUM, Fleming. 

 Ccecum trachea et imperforatum, Montagu. 



Animal cylindrical, arcuated, externally pure white ; the mantle 

 is very thick and fleshy, fitting the shell closely, and not extend- 

 ing beyond its anterior margin ; the body is elongated and slender, 

 with a long flat head, which on all occasions is in advance of the 

 foot, and appears to assist in locomotion ; the fissure of the mouth 

 is vertical, and from the tenuity of the skin the pale red buccal 

 mass is distinctly visible, the corneous plates of which are of 

 light yellow and subelliptical form ; the tongue was not detected, 

 though, without doubt, one of the invariable spiny character 

 exists. 



The tentacula are short, rather thick, subcylindrical, setose, 

 and slightly clavate at the extremities ; the eyes are very minute, 

 black, not raised on any kind of pedicle or eminence, and placed 

 nearly in a line with the tentacula at a short distance from their 

 bases, and if there is a divergence therefrom the tendency is ex- 

 ternal. 



The slender neck, as in most of the other Gasteropoda, is fur- 

 nished with longitudinal ridges, and in this species on each side 

 of its centre, there are two frosted, pale yellowish white, con- 

 tiguous raised lines forming a very decided canal or groove, the 

 points of which terminate anteriorly at the immediate base of the 

 eyes, and posteriorly at the furthest end of the neck, on the left 



