276 PROCEEDINGS OF THE ACADEMY OF [1893. 



I have seen no specimens of either the type or the variety, which 

 also has been regarded as a species, and am unable to judge about 

 them. 



KEY TO SPEdES OF VALLONIA. 



It is necessarily difficult to give a synopsis of the species of Val- 

 lonia based on the shell alone. The characters are quite interwoven 

 among the groups and species, and several attempts to found natural 

 groups upon one, or even a few prominent features proved to be 

 failures. Yet there are such natural groups, though not well- 

 defined, and the following table may serve to characterize t hem 

 and the subordinate groups, at the same time affording a means of 

 identifying specimens, definitely or approximately, without going 

 over all the descriptions. 



Group I (of pulchella'). Aperture crescentic, forming | to f of 

 a circle (not transversely elongated), with ends of margin distant, 

 little or moderately inclined and oblique; suture not markedly 

 descending to the aperture or not more so than the last whorl ; shell 

 of medium size; surface rarely or never ribbed ; nucleus, as a rule, 

 smooth (?). 30 



A. Last whorl not, or scarcely descending 



1. Peristome with a strong white lip, 



a. Peristome decidedly everted ; shell and umbilicus rather 

 symmetrical; surface finely striate pulchella. 



aa. Peristome scarcely everted; shell and umbilicus elongate, 

 surface smooth or very finely striate ; spire small and low 



excentrica. 



2. Peristome Avithout a lip, little everted ; whorls 4-4? diam. 2*5- 

 3 mm. adela. 



B. Last whorl gradually and steadily descending in toto, peristome 

 not everted ; lip thin or wanting 



1. Surface microscopically striate, appearing almost smooth; lip 

 thin or wanting declivis. 



2. Surface with fine membranous ribs, peristome straight and 

 thin, without a lip pollinensis. 



Group II (of costata). Aperture almost circular or transversely 

 elongate, with margins approximate ; peristome distinctly everted, 

 with a white lip ; last whorl moderately or not descending in front, 

 suture more descending, surface (as a rule) with distinct ribs or rib- 

 stripe. 



30 In adela and pollinensis the nucleus is unknown. 



