Mr. W. Clark on Caecum trachea and C. glabrum. 183 
The generic term Cecum appears to be somewhat objection. 
able in point of significancy. On the discovery of the animal I 
proposed to my friend Dr. Goodall, the late Provost of Eton, the 
generic appellation of Dentaliopsis, which I think I also men- 
tioned to Mr. Jeffreys of Swansea; but Dr. Fleming is in posses- 
sion of the field, and has the undoubted priority, and I may say, 
owing to my own neglect, in not launching the genus : 
ar ELOSHE EO sere « feci, tulit alter honores.” 
Caecum glabrum, Montagu. 
After a research, in which I almost despaired of success, I have 
had the good fortune to meet with two living vivacious specimens 
of this species in the coralline zones of the Devonshire coast, off 
Budleigh Salterton, six miles from the shore, in ten fathoms 
water. 
To describe the organs of this animal would only be a repe- 
tition of what has been said on Cecum trachea; I will only reca- 
pitulate them and notice the modifications thereof. 
The brown ovarium, light green liver, and the rectum with its 
contents of formed pale-brown pellets extending from the pylorus 
to the doubling amongst the folds of the liver, were distinctly 
visible through the transparency of the shell. The stomach, 
body and neck were of the purest white; the lines forming the 
canal or groove in the neck are less developed than in the former 
species ; the buccal mass is of the palest blush colour, and the cor- 
neous plates of the most delicate and lghtest green; the spiny 
tongue was not seen ; the same default occurred in Cecum trachea, 
probably from its white colour and extreme slenderness ; it doubt- 
less exists; the mantle is thick, circular and muscular, closely 
fitting the shell; the eyes are precisely fixed as in C. trachea; 
the very minute branchial leaflet is of the palest rose-colour, 
but the mantle must be removed to see it, owing to its extreme 
tenuity. 
I now come to those organs in which there are some variations : 
the tentacula, as in its congener, are frosted white and setose, 
but they appear to be proportionably longer, slenderer and more 
clavate at the tips; these variations however are scarcely appre- 
ciable. The foot is very short, truncate in front, rounded be- 
hind, and carried much more laterally in this species than in 
C. trachea ; and on its posterior upper part is the most differen- 
tial point in the animals, the curious operculum, which is circu- 
lar, and has six or seven spiral gyrations of a pale yellow, but 
instead of being concave or flat without and conical within, as in 
C. trachea, it isin both respects the reverse. Represent to yourself 
the flat spiral circular operculum of the last species, pushed out 
from its inner surface, or inverted, and thus forming a cone of 
