M. Desliaycs' Monograph of Denialium. 177 



The whole of the anterior part of the animal is inclosed in a fine mem- 

 brane which is fixed posteriorly to the origin of the foot, and is free in 

 •front, where it is thickened in its circumference and perforated in its cen- 

 tre : this M. Deshayes regards as the mantle. The thickening is formed 

 by a circular sphincter, which during its contraction wrinkles the skin, 

 and closely embracing in its opening the extremity of the foot, thus pre- 

 vents any communication with external objects. According to M. d'Or- 

 bigny,jun., who has supplied a drawing of the living animal while ex- 

 panded, in this state the dilated lobes of the foot resemble a flower, the 

 undulated and small corolla of which supports in its centre a pistillum 

 thickened towards its middle, and pointed at its free extremity, ,^ 



Such are the parts externally visible of the animal of Dentalium. To 

 reach the other organs the mantle may be slit down the middle of its dor- 

 sal surface, and separated from its insertion lo the right and left, for the 

 purpose of turning it downwards and to the right. We have then before 

 us the foot, the head, and the branchiae. 



The foot is elongated, subcylindrical, slightly conical, and flattened from 

 above downwards ; it is fleshy throughout, and is situated at the inferior 

 and anterior part of the head, having its upper and under surfaces de- 

 pressed in their middle into a slight groove. Its anterior extremity is the 

 largest, having its centre occupied by a kind of conical nipple, which is 

 broader at its base, being there partly covered by two small crenate late- 

 ral lobes, their notches corresponding with the grooves of the foot. The 

 posterior extremity has an appearance of bifurcation, owing to the attach- 

 ment it affords to the retractor muscles ; its middle part projects slightly 

 into the abdominal cavity, supporting the stomach and the other princi- 

 pal viscera. ; .> 



The head, which consists only of a mouth, is situated superiorly at the 

 hinder extremity of the foot. It is bell-shaped, and flattened from before 

 backwards. On its sides appear two black points, which might be mis- 

 taken for eyes, but are actually the jaws placed within the mouth, and 

 visible through the thin substance composing it. These jaws are sphe- 

 rical, horny, rough on their outer surface, and cleft in the middle, strongly 

 resembling a very small bivalve shell. The lips are also two, deeply cleft 

 at the margin, or rather furnished each with three pair of labial tentacula, 

 those of the posterior lip, and especially the middle pair, being cousi- 



