THE NAUTILUS. 5 



but the distal margins remain practically entire; sutural 

 plates narrow, the sinus shallow with entire margin ; a brown 

 streak on each side of it internally but the rest of the interior 

 white; external sculpture of the intermediate valves with 

 lateral areas but no defined jugal tract; the surface micro- 

 scopically reticulate with, on the central and pleura! tracts, 

 rather sparse slender bluish beaded longitudinal threads on a 

 brownish ground, about 15 threads on each side with wider 

 interspaces; lateral areas with two to four similar threads of 

 which not more than two run the whole length of the area, 

 the others being irregularly broken up and short ; the anterior 

 valve with about 20 similar threads, tending to pairs; the 

 posterior valve with a feeble subcentral mucro, in front of 

 which it is threaded like the pleural tracts, behind it there 

 are about a dozen sparse feeble radial threads. There are no 

 eyes or visible sense organs on the surface of the valves. 

 Length of specimen (after soaking) 23; breadth 16; height 

 8 mm. U. S. Nat. Mus. Cat. no. 333091. 



WHAT IS THE TYPE OF ANCYLASTBUM BOURGUIGKAT 1 



BY BRYANT WALKER. 



In a paper recently published in the Proceedings of the 

 Malacological Society (XIV, 1920, p. 86), Messrs. Kennard 

 and Woodward, after stating that in their opinion the type of 

 Ancylus of Geoffrey was the Patella- lacustris of Linne, and 

 that as that species is the type of Beck's Acroloxus, the latter 

 consequently becomes a synonym of Ancylus s. s., suggest 

 that as fluviatilis Mull, must be placed in a distinct genus, 

 "recourse must be had to the subgeneric name of Ancylas- 

 trum, proposed by Bourguignat in 1853 and that name must 

 now be raised to generic rank." 



Assuming that the premises of the authors are correct, 

 which is by no means free from doubt, the question is at once 

 raised as to whether Ancylastrum Bgt. can properly be used 

 for the group typified by the European fluvia-tttis Mull. 



If so, it is evident that the Tasmanian species represented 



