On Prophysaon^ etc. 297 



Before deciding that this slug is new to science we com- 

 pared it with the descriptions of Avion foliolalus, Gould 

 (Terr. Moll. U. S., II, 30, pi. Ixvi, fig. 2) and Avion? An- 

 devsonii, J. G. Cooper (Proc. Phila. A. N. S., 1872, 148, 

 pi. iii, fig. F, 1-5). Our species cannot be identical with 

 the former, which is described as &\\ Avion, with "a conspicu- 

 ous pit, which probably was occupied by a mucus gland" at 

 the truncated tip of the tail. The areolae formed by the retic- 

 ulating lines of A. foliolatus are said to have their surfaces 

 indented by leaf-like markings, no doubt the same as the 

 granulations between the reticulations of Pvophysaon. In 

 our genus, however, the granulations seem less regularly 

 arranged. The figure of Avion foliolatus* shows, also, a 

 larger mantle, which leaves a much smaller space between 

 its lower margin and the longitudinal furrow above the foot, 

 than does the mantle in our species. 



At first sight it seemed as if our species might be identical 

 with Avion? Andevsonii, but that species is described and 

 figured with a distinct locomotive disk, with the respiratory 

 orifice perceptibly anterior only when the animal is fully 

 extended, with a jaw having 20-30 ribs, with a minute 

 caudal mucus pore and with the generative orifice half-way 

 between the tentacle and the mantle, all of which does not 

 apply to Pvophysaon HemphiJU. 



We deem it necessary, therefore, to find a specific as well 

 as generic name for our slug, and take pleasure in adopting 

 that of Mr. Henry Hemphill, who has given us so much 

 assistance in our studies of the land shells of the Pacific 

 Coast. 



On the Generic Characters of Ariolinistx. 

 Having received from Mr. J. G. Anthony, of the Cam- 

 bridge Museum of Comparative Zoology, a specimen of the 

 true AvioUmax, probably the A. Califovnicus, we are en- 



*Fig. 6 of the Ex. Ex., shows the respiratory orifice behind the centre of the mantle 

 edge. 



