542 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



so tapering below as to give the shell almost a fusiform outline: this, how- 

 ever, may be to some extent due to distortion. 



This species seems to be related to the recent Bulinus hypnorum, but 

 has a proportionally broader body-volution, and not quite so produced a spire. 

 These differences, however, are not near so marked as would appear from our 

 figures, which are represented as having the body-whorl too wide and the 

 spire too short. 



Locality and position. — Lignite series of the Fort Union group, three 

 miles below Fort Union, Dakota; probably Lower Eocene. 



Bulinus! rhomboidens, M. & H. 



Plate 43, fig. 17. 

 Pht/sa rhomhoidea, Meek and Hayden (18. r >6), Proceed. Acad. Nat. Sci. Pbilad., VIII, 119. 



Shell small, rhomboid-subovate, narrowing abruptly from the middle to 

 the apex of the spire, which is rather short and pointed ; volutions four and 

 a half to five, convex, last one rather large, and moderately ventricose ; suture 

 well defined ; aperture narrow-subovate, angular above, and narrowly rounded 

 below; columella tortuous, and apparently forming a small fold; surface 

 marked by fine, obscure lines of growth. 



Length, 0.26 inch; breadth, 0.15 inch: length of aperture, 0.16 inch; 

 breadth of same 0.07 inch : apical angle slightly convex, divergence 

 about 60°. 



This may possibly lie only a distorted specimen of the last-described 

 species; but it seems to have a shorter, more abruptly-attenuated spire, and 

 a rather more decidedly ventricose body-volution. Both specimens are dis- 

 torted, however, so that the means of comparison are by no means satis- 

 factory. 



There is in the collection, from the same locality and bed, a much larger, 

 broken, and distorted specimen," that may possibly belong to this species; but 

 additional collections are necessary to clear up the question of its relations to 

 the species here described. 



Locality and position. — Same as last. 



