784 PROCEEDINGS OF THE ACADEMY OF [DeC. 



A large series was collected. It resembles S. vanattai in shape, l)iit 

 is about double the linear dimensions of that species, and has a propor- 

 tionally larger lip notch or sinus. In S. nicoleti the periphery is less 

 strongly angular, the spiral lirse more widely spaced and the operculum 

 sharply granulose externalh^ The specimens have been compared by 

 Prof. W. H. Dall with the unique type of his »S. hidalgoana from Encar- 

 nacion, Hidalgo, and pronoimced to be identical. Since that species 

 was described from a dead, bleached specimen, I have given a new 

 description of a fresh shell, and figures of a specimen from near 

 ^'ictoria. 



SPH^RIID^. 



Crosse and Fischer have shown that the species of Sphariiun known 

 from ^lexico fall into three subgenera: Sphcerium s. str., Muscidium 

 Link (Calyculina Cless.), and Eiipera Bgt. The third group has been 

 raised by von Martens to generic rank. No species of Eupera was taken 

 by ]\Ir. Rhoads, but the other groups mentioned are represented in his 

 collection by numerous forms, the study of which necessitates some 

 revision of the group. 



The following Mexican and Central American species have been 

 admitted in the Biologia Centrali Americana: 



S. triangvlare Say. 



S. suhtransversum Pme. 



S. martensi Pils. 



S. luridum Marts. 



S. costaricanum Marts. 



The last-mentioned species is not known to me by sj^ecimens. From 

 the description and figures it seems to be very different from the others, 

 and a good deal like a Pisidium. 



The other Mexican species are very well characterized and readily 

 distinguishable. They may be tabulated as follows: 



a. — Shell very thin and fragile, delicately striate ; beaks usually showing 

 a distinctly defined prodissoconch. 

 b. — Shell oblong, the alt. about three-fourths the length, diam. 



half the length or less, S. suhtransversum. 



h' . — Shell subrotund, the alt. exceeding three-fourths the length, 



diam. more than half the length »S^. novoleonis. 



a' . — Shell varying from thin to moderately strong, striate or costulate, 



without distinct prodissoconch. 



h. — Beaks regularly costulafe. Alt. more than three-fourths the 



length ; diam. decidedly over half the length ; hinge-line more 



arcuate than the basal margin; solid, with stout lateral 



teeth and rather coarse sculpture, . . . S. triangularc. 



