Tornatellidse, and Pyramidellidse. 447 



I considered the respiratoiy cavity having its walls lined with an 

 anastomosing network 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 fsecal matters ejected from a dilata- 

 tion in the mantle lining the aperture. It must not be supposed 

 that I have mistaken this orifice for the termination of the rec- 

 tum : that organ ends wdthin the mantellar dilatation, 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 ^th of an inch long, prevented 

 me observing the periodic dilatations. The facts I have stated 

 appear to be decisive, that the animal respires free air ; in addi- 

 tion, 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 therefrom, 

 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 hermaphroditism to the Helices, that 

 of mutual congression. All these facts favour the opinion that 

 the animal breathes free air. Those I examined inhabit 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 tliat these animals are submerged for only a very small 

 part of the year proves nothing as regards the plan of respiration, 

 as the Rissoa ulvce and minute LittorincB adhere constantly to 

 the outside of the bases of the stones under which the Conovuli 

 are found, and are not more submerged than they, and yet 

 these animals are decided pectinibranchiata, which nevertheless 

 appear to have the power of living in free air with almost equal 

 facility as the pulmonifera, and perhaps by constant exposure to 

 the atmospheric air their branchiae acquire the capability of ex- 

 tracting oxygen therefrom. Though the C bidentatus are so 

 little submerged, the places they lie in are always humid from 

 the influences of the tidal waters. 



The Conovulus denticulatus is rarely found at Exmouth : I 

 have not seen the animal ; it will be desirable to observe if tlie 



