180 Mr. W. Clark on Ceecum trachea and C. glabrum. 
XX.—On the Animals of Ceecum trachea and C. glabrum. 
By Witiram Crark, 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 Cecum 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 im 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” of these mollusca. 
Cacum, Fleming. 
Cecum 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 mvariable spmy 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 
