Mr C. Collier oti Univalves. 227 



and many of the Helices and Neritoe ; thin and flexible, but 

 narrow, short, and attached to the posterior parts, in the spe- 

 cies of Co7iits, and some species of Buccinum (as B. vibex, B. 

 Cassis) ; rocky and convex in some Turbines ; irregular in Ser- 

 pula lumbricalii. 



The operculum is not found in the genera Cyprem, Valuta 

 Haliotis, Patella, nor in certain species of other genera such 

 as Btdla Ovum, B. ampulla, B. Ficus ; Buccinum Harpa, and 

 its varieties, B. Dolium ; nor in Serpula aquaria *. 



That muscular mass which serves for the support and pro- 

 tection of the more important organs of the animal, for motion, 

 and for changing the possition of the shell, is denominated by 

 naturalists, without reference to the literal signiflcation, the 

 foot. 



It contains the mouth, brain, oesophagus, and auxiliary 

 glands, and is the part by which the animal attaches itself, as 

 with a sucker, to other objects, or creeps along by its muscular 

 contractions. In the Strombus, the extremity of the operculum 

 is a point (Tappui, from whence the shell is jerked forward on 

 the smaller foot, or thrown over upon its aperture. In the 

 Murex, the shell is whirled round upon its back, as upon a 

 pivot, with the aid of the operculum ; or when its aperture is 

 placed downwards, the animal creeps slowly forwards, by means 

 of the sucker only. 



It is of a circular or oval form, and exterior to the opercu- 

 lum in the genera Murex, Turbo, Helix, Nerita ; in some 

 Buccina (as B. patulum and spiratum;) aiid all fusiform 

 shells, including Trochi. It is double, by a process, serving 

 for adhesion, coming off from that which bears the operculum, 

 in Strombus ; oblong or oval, in Conus, and in Buccinum Vibex 

 and Cassis. 



" The assertion extends only so far, of course, a.s my opportunity of know- 

 ing. I have never seen one species of the Argonauta, Nautilus or Dentalium, 

 with the animal in it, nor several of the other genera, as Bulla Zebra and 

 Volva ; Valuta Glans, Papalis, and Auris-midw ; Turbo unguis and Scalaris ,• 

 Trochus zixyphinus and dolalratus ; Helix columna ; nor many Neril<B. It may 

 also be observed here, that most fusiform species of all families, (for example, 

 Bmcinum strigilatum ; Strombus palustris, Trochus Turritus, Turbo terebra and 

 ejtoletusj, are connected by structure, and therefore often differ from those 

 with which they are associated by the form of the shell. Buccinum maculalum, 

 however, is -jomcwhat like Ji. Vibcr. 



