THE NAUTILUS. 41 



the keel; peristome simple, the margins converging; parietal callus 

 short and rather thin. 



Alt. 9, diam. 21-22 nam. 



Mission Mountains, Montana (Prof. M. J. Elrod). 



This species holds toward P. strigosa a relationship like that of 

 P. cumberlandiana toward P. altemata. Except in being more 

 widely umbilicated and with ;i wider last whorl, it would be well 

 resresented by the published figures of Epiphragtnophora circum- 

 carinata (Stearns). The ribs are less regular than in the typical 

 form of P. idahoensis, but are equally strong. None of the wonder- 

 ful series of strigosa varieties discovered by Hemphill approach this 

 form ; which could not, with present information, be considered a 

 sub-species of strigosa. It is, like idahoensis and hayde?ii, doubtless 

 the terminal member in a differentiation-series from the strigosa 

 stock, but the connecting links are wanting tn the recent fauna, so 

 far as present collections show. 



It is named in honor of Prof. M. J. Elrod, of the University of 

 Montana. 

 Helicodiscus Eigenmanni n. sp. 



Shell similar to H. lineatus, but attaining a much greater size, the 

 umbilicus much smaller in comparison with the diameter of the 

 shell. Whorls 4| to ">, strongly lirate spirally. Aperture more 

 lunate, embracing more of the preceding whorl, usually armed with a 

 pair of small teeth within, as in H. lineatus. Umbilicus rather deep 

 and cup-shaped. Alt. 1.9, diam. 4.8 mm., umbilicus 2 mm. wide. 



Beaver Cave, near San Marcos, Hays Co., Texas. 



This species was collected by Dr. C. H. Eigenmann, the well- 

 known writer on fish morphology. 



The specimens are very uniform in character, differing markedly 

 from the common and wide-spread H. lineatus. The latter shows 

 but little variation throughout its enormous range, and so far as I 

 can see from a very large series, there is nowhere a tendency to be- 

 come more narrowly umbilicated. The present form has been found 

 only in the cave mentioned above, and may possibly be a modifica- 

 tion induced by underground life, although until the immediate sur- 

 roundings of the cave are searched, it would be unsafe to more than 

 suggest this. I find only the ordinary H. lineatus from other Texan 

 localities. Nothing like H. Eigenmanni occurred to me at San 

 Antonio, New Braunfels, or Austin. 



