180 BRITISH MOLLUSKS. 



cording to the observations of British conchologists, are sometimes 

 closely lineated, sometimes nearly smooth. French writers consider 

 that there are three, if not four, species of Acme, and that a marginal 

 cleft in the upper corner of the aperture, which in some is deeply 

 cut, in others almost obsolete, is of sufficient importance to be 

 selected as a basis of subdivision. We cannot satisfy ourselves that 

 there is more than a single species, unless exception be made in 

 favour of a more elongated eight-whorled species, A. spectabilis of 

 Hossmassler. Acme lineata is pretty generally diffused throughout 

 Europe in wet places, under stones in drains, or under moss or de- 

 cayed leaves. 



M. Moquin-Tandon describes Acme as being rapid in its move- 

 ments and very irritable. Mr. Jeffreys remarks that a living speci- 

 men which he observed in the North of Ireland did not seem to be 

 shy or inactive while kept in the shade, but when exposed to the 

 glare of the sun it immediately shut up and disappeared. Dr. Gray 

 says, that the animal walks with its shell nearly perpendicular, 

 twisting it round in a very odd manner, and then letting it suddenly 

 fall again. The operculum, which is horny, is composed of fewer 

 whorls than the shell, only about two and a half, and is sunk rather 

 deep within the aperture. 



Order II. BRANCHIFERA. 



Respiratory organ gills of filaments or lamella for the respiration of 



water. 

 The water-breathing operculated Cephals are more numerous 

 than those which respire air. Of the latter, as we have just seen, 

 there are only two British species, of two genera, Cyclostoma and 

 Acme ; of the former we have nine, illustrative of five genera, 

 Assiminea, Bythinia, Paludina, Yalvata, and Neritina. The 

 branchial chamber occupies its usual position on the right side 

 of the animal, near the head. In Assiminea and Bythinia, the 

 branchiae form a row of wrinkled lamellse. In Paludina, they con- 

 sist of three rows of filaments, and the entrance to the chamber is 

 by a tubular fold of a fleshy lobe immediately behind the right ten- 

 tacle ; on the opposite side there is a corresponding rudimentary 

 lobe, which, in Ampullaria, an amphibious genus of this family 

 belonging to a warmer climate, developes into a siphon for the con- 

 veyance of air to a pidmonary chamber. Mr. Berkeley has stated his 



