370 MEXICAN BOUNDARY SHELLS— DALL. 



Two specimens from Lake Palomas, northeastern Mexico, collected 

 by Dr. ]\rearns. No. 130016, U.S.N.M. 



One of the specimens has the latter third of the last whorl free 

 from the body, as in Lyogyrus, a somewhat common pathologic condi- 

 tion in species of this and allied genera, but in the other and evidently 

 normal specimen the peristome is quite free from the adjacent body 

 whorl, not appressed thereto. Neither example retained the operculum 

 or dried soft parts, and therefore the generic reference can not be veri- 

 fied by examination of the dentition, but the form of the shell is that 

 of a Bythinella rather than an Amnicola. It is a stumpier shell than 

 B. hiimeyi, Tryon, and has far less inflated whorls than B. hrevissima, 

 Pilsbry, but these two, among United States species, are conchologic- 

 ally its nearest allies. Of the short-spired Mexican forms Amnicola 

 orizabemis, Crosse and Fischer,' is totally diverse, although the figures 

 in their work look somewhat like this species. .1 . (juutemcdenKis, Crosse 

 and Fischer, is larger, with a relatively smaller aperture [PilsbryJ. 



Genus SPH^^RIUM, Scopoli. 

 SPHiJERIUM SOLIDULUM, Prime. 



Numerous specimens of this species were obtained in Arizona from 

 the San Bernardino Elver. 



Genus PISIDIUM, Pfeiffer. 

 PISIDIUM COMPRESSUM, Prime. 



Collected by Dr. Mearns in the San Bernardino River, Arizona, and 

 Lake Palomas, south of the boundary line in the Mimbres Valley, 

 northeastern Mexico. 



PISIDIUM ABDITUM, Haldeman. 



San Kafael, New Mexico; Ashmuii. 



Genus UNIO, Retzius. 



The notes upon this group and Anodonta are by Mr. Charles T. Simp- 

 son, of the United States National Museum. 



UNIO COUCHIANUS, Lea. 



Vnio rutwhianiis, Lea. .Jouru. Acad. Nat. Sci., IV, p. 371 ; Obs. on tiie Gemis Unio, 

 VIII, p. 53, pi. Lxvi, fig. 196. 

 This rare species was described by Dr. Lea from half a dozen odd 

 valves sent to him by the Smithsonian Institution, which were procured 

 by Lieut. D. N. Couch, U. S. A., from Dr. Beiiandier's collection. The 

 shell has the general form of an iutlated r.asjferriniKs, but is much less 

 tuberculate. Dr. Lea describes it as smooth, but a careful examination 



' Plate L, figs. 4a, 4b. 



