PEDIPES. 301 



mals to the powers of an excellent microscope, I am enabled 

 to say, that I found no traces of a regular pectinated mem- 

 brane ; but when the dissection turned out well, there ap- 

 peared, as in the Helices, what I considered to be the respira- 

 tory cavity, having its walls lined with an anastomosing net- 

 work of vessels ; one side of this membrane abutted on the 

 rectum and the canal of the sac of viscosity. The strongest 

 support that this is the true respiratory organ is, that I 

 observed in several individuals large cylindrical masses, not 

 pellets, of red-brown sandy faecal matters, ejected from a 

 dilatation in the mantle lining the aperture. It must not be 

 supposed that I have mistaken this orifice for the termination 

 of the rectum : that organ ends within the mantellar dilata- 

 tion, exactly as in Helix, in which the respiratory orifice 

 dilates to receive air as well as to emit the rejectamenta. This 

 dilatation in the present species has not the aspect of the 

 terminus of a rectum ; it is a simple oblong fissure, which 

 instantly closes and is lost to view when the faeces are passed. 

 The continual change of posture of these animals, not one of 

 them Jth of an inch long, prevented my observing the periodic 

 dilatations. The facts I have stated appear to be decisive 

 that the animal respires free air ; in addition, it has the cord- 

 like margin of the mantle, as in the Helices, around the 

 aperture of the shell, and the figure and course of the large 

 conspicuous intestine is also as in Helix. 



The animal when put into water instantly escapes there- 

 from, apparently with the view of breathing free air. All 

 the animals exhibited the ovary : this circumstance almost 

 amounts to proof, that they possess a similar hermaphro- 

 ditism to the Helices, that of mutual congression. Those I 

 examined inhabited a bank wall, that for ten days out of 

 thirty is covered by the sea for three or four hours out of the 

 twenty-four ; they are found lying at the bottom of stones 

 which are imbedded in a red sandy soil, and have not been 

 disturbed for years; the detached stones at the base of the 

 wall under which they are found are buried from 3 to 6 

 inches, and require force to raise them. 



The fact that these animals are submerged for only a very 



