342 UNITED STATES GEOLOGICAL SURVEY OE THE TERRITORIES. 



but its channeled suture, and more rounded aperture, with its inner lip, as it 

 were, disconnected from the umbilical region, are characters that forbid its 

 reference to that genus. 



Mr. Conrad has referred a Cretaceous species doubtfully to Dr. Lea's 

 genus Tuba, that seems almost certainly congeneric with the type of this 

 genus. His specimen appears not to have been in a condition to show the 

 aperture. In our type, however, the aperture is clearly seen to be rounded 

 instead of angular below, as in the species upon which Dr. Lea founded his 

 genus; which is also described as having its columella thickened and reflexed 

 at the base. Mr. Conrad has also proposed, in the North Carolina Report 

 (Appendix, page 12), a genus Callonema, that appears to me very closely 

 related to this. 



So far as yet known, this seems to be a Cretaceous genus only, though 

 it may also include some Tertiary forms. 



Spironcma tenuilineata, M. & H. (sp.). 



Plate 32, figs. 9, a, b, c. 



Turbo tenuiVmeatus, Meek ami Hayden (1856), Proceed. Acad. Nat. Sci. Philad., VIII, 64. 

 Xpironema tenuilineata. Meek (1864), Smithsonian Check-List N. Aui. Cret. Fossils, 19 and 35. 



Shell obliquely subovate, comparatively thin ; spire forming about half 

 the entire length, apparently rather acute at the apex; volutions about five 

 aud a half, prominently convex, last one rounded and somewhat produced 

 below ; surface marked with fine lines of growth, which are crossed by 

 stronger, irregular, revolving lines, about equaling the grooves between; 

 much finer, obscure, revolving striae may also sometimes be seen by the aid 

 of a magnifier, upon and between the larger lines. Aperture a little oblique, 

 very nearly ovate, but a little straighter on the inner than the outer side : 

 umbilicus small. 



Length, 0.79 inch; breadth, 0.60 inch; apical angle regular, 68°. 



The revolving lines give this shell a rather neatly ornate appearance. 

 They are smallest on the upper part of each whorl, and increase in size 

 below. Some of those near the middle of the body-whorl are divided by a 

 small, impressed line along the middle. The excavated character of the 

 suture gives a slightly-truncated aspect to the summit of the whorls, and a 

 turreted appearance to the spire. 



From Tuba', bella of Conrad, mentioned in the remarks under the 



