^'♦ 



The Nautilus. 



Vol. XXIII. AUGUST-SEPTEMBER, 1909. No. 4 



MOLLUSKS FROM NORTHEASTERN MEXICO. 



BY H. A. PILSBRT. 



These shells were collected by Mr. A. A. Hinkley during the past 

 winter, in the state of San Luis Potosi, Mexico. The Panuco river 

 system has proved to be unexpectedly rich in fresh-water mollusks, 

 having a fine group of Unionidce, a remarkable lot of Pachychili, a 

 new genus of PleuroceratidcB, a Gimdlachia, and various interesting 

 Amnieolidct. Among the latter there are several genera unlike any 

 known American forms, and related to genera of the Old World. 

 I have elsewhere called attention to a little snail found by Mr. 

 Hinkley last year, Coilostde tampicoensis, which is closely allied to 

 species of Spain, Syria and Arabia, but of a genus not before known 

 in the western world. The two genera following, Emmericia and 

 Pterides, seem to be similarly allied to European groups, and are 

 certainly quite unlike any other American Amnicolidct yet known. 



Emmericia. 



This genus was established by the late Professor Spiridion Brusina, 

 of Agram, for a group of fresh -water snails resembling Bithynia in 

 shape, but having a paucispiral operculum and a thickened, ex- 

 panded lip, behind which there is a rounded ridge or wave. The 

 species inhabit Dalmatia and the adjacent region around the head of 

 the Adriatic Sea. The commonest and typical species is E. patula 

 (Brumati). 



Several species found in the state of San Luis Potosi by Mr. 

 Hinkley are so close to Emmericia in conchological characters that 

 I do not feel justified in separating them generically from that group, 



