190 PALAEONTOLOGY. 



Planorbis spectabilis var. Utahensis, Meek. 



Plate 17, tigs. 14, 14 a, 14 6, aud 14 c. 



Planorbis Utahoniis, Meek (1860), Proceed. Acad. Nat. Sci. Pliilad., XI f, 314; and 

 (1870) ill Col. Siuipsou's Itepoit Expl. across the Great Basiu of Utali, 305, pi. v, 

 fij;s. S a, b, c. 



Shell large, discoidal ; upper side nearly flat, or sometimes slightly 

 concave in the middle; periphery rather narrowly rounded or subangular; 

 umbilicus moderately large, rather deep; volutions five and a half to six, 

 increasmg gradually in size, wider than high, and moderately convex both 

 above and below, each about one-half enveloped on the under side, and less 

 than one-fourth on the upper, by the next succeeding turn. Surface and 

 aperture unknown. 



Greatest breadth of a large specimen, about 1.19 inches; height, 0.35 

 inch. 



This form is much like the last, but differs in having a deeper umbil- 

 icus, and proportionally wider volutions, which are generally distinctly 

 wider than high, instead of the reverse. It seems to be quite sunilar to P. 

 rotundatiis of Brongniart, from the Paris Basin ; but none of the specimens 

 show any traces of the angle around the under side of the volutions, gener- 

 ally seen in that shell, as illustrated by Deshayes in the supplement to his 

 great work on the fossils of the Paris Basin. Among our known recent 

 American species, it is perhaps most nearly represented by P. subcrenatus 

 of Carpenter, from Oregon ; but it evidently shows a greater number of 

 volutions on the upper side, and certainly seems not to have had as strong 

 marks of growth as that shell. It is true the specimens are all casts; but it 

 seems scarcely probable that if it had ever possessed these lines there would 

 have been no traces of them left. 



The type-specimens of this form certainly have much more depressed and 

 proportionally wider volutions than the last; and if we could be quite sure 

 that this is not, at least in part, due to accidental pressure, there would be 

 scarcely any reason for doubting that it is specifically distinct. 



The form referred to this species by Dr. White, in his report on Lieu- 

 tenant Wheeler's collections, ])late xxi, fig. 8, seems to me to agree more 

 nearly with the last. 



