GASTROPODA. 207 



MOLLUSCA 



Class GASTROPODA 

 Subclass Streptoneura 

 Order Ctenobranchiata 

 Suborder Platypoda 

 Superfamily Taenioglossa 

 Family Capulidae 

 Genus Platyceras Conrad 

 Platyceras pentalobus Hall 

 Plate 54, figures 10-20 

 Platyceras pentalobus Hall, 1859, Pal. N. Y., vol. Ill, p. 319, pi. LVIII, figs. 7a-c, 1861. 

 Description — "Shell obliquely subconical; spiral with about two volutions; apex 

 and upper volution smooth and rounded, becoming plicate on the last volution; plica- 

 tions four, five or more; peristome simple. Surface marked by fine transverse striae, 

 which are strongly undulated in passing over the plications. 



"[Remarks] — I have not been able to trace this species through its gradations of 

 form; but it is so different from the other species observed, that I can have no doubt 

 of its specific distinctness." — Hall, 1859. 



Remarks — The Missouri specimens referred to P. pentalobus present a gradational 



variation as follows: Apex above to below upper surface of body whorl; whorls about 



1J^ to about 3, all contiguous to part of body whorl free; lower surface of body whorl 



flattened to rounded; upper surface of body whorl rounded to subangular to flattened. 



Dimensions — Range in size of shells indicated by figured specimens. 



Platyceras sp. 

 Plate 54, figures 21, 22 

 Description — Single specimen with about 2 contiguous whorls, apex below upper 

 surface of body whorl, body whorl with median ridge; peristome incomplete, upper 

 portion with shallow sinus, outer lip with deep sinus, character of lower portion un- 

 determinable; surface marked with undulating growth lines. 



Remarks — This shell resembles P. tenuiliratum Hall 1 but the apex is below the upper 

 surface of the body whorl, and the outer lip is deeply sinuate. 



Platyceras ? sp. 

 Plate 54, figures 23, 24 

 Description — A portion of a whorl is doubtfully referred to this genus. 



Genus Diaphorostoma Fisher 



Diaphorosloma sp. 

 Plate 54, figures 25, 26 

 Description — The specimen is an internal cast of a shell of about 2Yi whorls which 

 resembles D. depressum (Hall) 2 but is smaller. 



'Pal. N. Y., vol. Ill, p. 317, pi. LVI1J, figs. 1-5; pi. LIX, figs, 6a, b, 1859, 1861. 

 =Pal. N. Y., vol. Ill, p. 301, pi. LV, figs. 4a, b., 1859, 1861. 



