1903.] NATURAL SCIENCES OF PHILADELPHIA. 779 



call V. strebeli, but base their conclusions upon the published descrip- 

 tions only. V. humeralis varies somewhat in the amount of flattening 

 l^elow the suture, but that character is always noticeable, and the early 

 whorls often appear angular in the middle on account of it. The 

 striation is rather irregularly developed, but always low, never sharp 

 as in V. sincera. Some specimens show a few very low subobsolete 

 spiral cords or threads near the periphery of the last whorl, but these 

 are exceptional. The base is indistinctly subangular around the um- 

 bilicus. ^Measurements are as follows: 



Alt. 4.2, diam. 5.2 mm., whorls 3f (L. Xochimilco). 



Alt. 4, diam. 5 mm., whorls 3^ to 3f (Strebel). 



Alt. 3.2, diam. 4.7 mm., whorls 3^ (L. Xochimilco). 



Alt. 3, diam. 4 mm., whorls 3^ (Say's type). 



I have treated this species at some length, because, with the excep- 

 tion of Strebel, none of the waiters upon this fauna have seen specimens 

 of Valvata from Mexico. 



Valvata humeralis pilsbryi Martens. PI. LII, figs. 5, 5a. 



Valvata humcTalis, specimens from Lake Patzcuaro, Pilsbrv, Proc. Acad. 



Nat. Sci. Phila., 1891, p. 326. 

 Valvata humeralis var. pilsbryi Martens, Biologia, p. 427, September, 1899 



(based upon the preceding reference). 

 Valvata humeralis var. patzcuarensis Pilsbry, Proc. Acad. Nat. Sci. Phila., 



1899, p. 392 (October 5, 1899). 



This form is smoother and more elevated than V. humeralis, but still 

 has an obtuse summit; the subsutural flattening of that species, while 

 noticeable on the spire of this, is minimized on the last whorl; and, 

 finally, the umbilicus is narrower, in specimens of the same diameter. 



Alt. 5.1, diam. 5 mm., whorls slightly over 4. 



Alt. 4.3, diam. 5 mm., whorls 3f . 



Alt. 4, diam. 4 m.m., whorls 3^. 



Lake Patzcuaro, Michoacan. Several hundred specimens were 

 taken by Mr. Rhoads in 1899. All were collected dead but in good 

 condition, covered with a light brown cuticle. A few of the freshest are 

 of a rather bright green color. 



Types of this variety are No. 61,444, A. N. S. P., collected by Heil- 

 prin and Baker in 1890. The varietal name patzcuarensis was proposed 

 by me before Prof, von Martens' work on the same form reached 

 America, but it is apparently of later date, if the signature lines of the 

 Biologia indicate the actual dates of publication. 



