570 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



with a divergence of 47°. Some crushed specimens show that it attained 

 nearly twice the linear dimensions of that from which the above measure- 

 ments were taken. 



The strongly angular character of the whorls in this species is so con- 

 spicuous a character as at once to distinguish it from all the other known 

 forms of the Upper Missouri country. The angle seems to be well defined 

 on all the whorls, particularly on the last or body-volution. Above the 

 angle, all the whorls are flattened with an outward slope, and below it the 

 under side of each slopes inward to the suture at an angle of about 90° 

 from the superior flattened side. The under side of the last turn slopes 

 inward from the angle, with a moderately convex outline. 



It is only provisional!} 7 that I refer this shell to the genus Goniobasis, 

 none of the specimens yet seen being in condition to show much more than 

 the mere form of its volutions. In its rather short conical form, and the 

 strongly angular character of its volutions, it does not agree well with the 

 known species of that genus, particularly in having the strong angularity 

 continued upon the body-whorl. Still, G. tortulosa, Anthony (sp.), regarded 

 by Mr. Tryon as only a variety of G. acutocarinata, Lea, does not differ very 

 materially in this respect. 



Mr. Tryon, to whom I sent plate 43, containing the figures of this spe- 

 cies, wrote that he thought it possibly a scalariform monstrosity of a Planor^ 

 bis. The fact, however, that we have several imperfect specimens, all agree- 

 ing in their characters, seems rather opposed to this view. A single fragment 

 exposing the under side of the body-volution of one specimen shows the lines 

 of growth to be strongly arcuate below the mesial angle, in such a manner 

 as to indicate a prominence of the outer lip below the middle, somewhat as 

 in Trypanostoma, Lea, or Lioplax, Troschel. Indeed, I am not sure that it 

 might not be more properly called Lioplax subtortuosa. Its true position, 

 however, can only be satisfactorily determined when more nearly complete 

 specimens can be examined. 



The foregoing wood-cuts give a more correct idea of the shell than the 

 figures on our plate. The specimen, however, has the lip broken so that we 

 cannot be quite sure that the aperture is represented exactly correct. 



Locality and position. — Mouth of Judith River, Judith River group; 

 probably belonging to t he closing period of the Cretaceous. 



