Mr. W. Clark on Caecum trachea and C. glabrum. 183 



The generic term Caecum 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 : 

 " Hos ego feci, tulit alter bonores." 



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 Ccecum 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 lightest green; the spiny 

 tongue was not seen ; the same default occurred in Caecum 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 is in 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 



