384 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



The genus Tunis seems to have made its appearance durring the latter 

 part of the Cretaceous epoch; but it was, so far as known, not numerously 

 represented until after the close of the Cretaceous period. During the 

 deposition of the Tertiary rocks, however, this genus was represented by a 

 number of species, and probably then attained its greatest development; 

 though many of the Tertiary shells referred to it under the name Pleurotoma, 

 belong to other allied genera, and not to this group as here defined. It is 

 quite abundant in our existing seas, however, and has a wide geographical 

 distribution. The species are said to be most numerous in Asiatic seas; and 

 are found at all depths from low tide to one hundred or more fathoms. 



Turris minor, E. & S. (sp.). 



Plate 31, figs. 9, a, b, c. 



Pleurotoma minor, Evans and Shuinard (1857), Trans. Acad. Sci. St. Loois, I, 41. 



Turris minor, Meek and Hayden (I860), Proceed. Acad. Nat. Sci. Philad.,XII, 41.— Meek (1864), Smith- 

 sonian Check-List N. Am. Cret. Fossils, 22. 



Shell small, symmetrically and moderately elongate-fusiform; spire 

 rather elevated, but not quite equaling the length of the aperture and canal ; 

 volutions about six or seven, convex, and somewhat angular around the mid- 

 dle ; last one not ventricose, narrowing gradually into the rather produced, 

 nearly straight, tapering canal; suture distinct; aperture lance-oval, angular 

 above, and tapering gradually below ; outer lip broadly prominent in outline 

 near the middle, somewhat retreating below, and again retreating above, into 

 the deep, rather wide, rounded sinus, between the suture and the most con- 

 vex part of the volutions ; surface ornamented by distinct lines of growth, 

 sometimes forming minute wrinkles just below the suture, and numerous 

 revolving lines, of which those below the mesial angle of the volutions are 

 larger than those on the flattened slope between the angle and the suture — 

 one directly on the angle being generally larger than any of the others; small 

 vertical costte are also seen on the upper turns of the spire. 



Length of largest specimen seen, 0.70 inch; breadth of same, 0.24 inch; 

 slopes of spire nearly straight, with a divergence of about 35°. 



The revolving lines mentioned above number about ten to twelve on 

 each volution of the spire; those on the upper flattened slope above the mesial 

 angle being not more than half as large as those below, and generally more 

 crowded. The little vertical costoe are only seen near the summit of the 

 spire, and consequently would not be preserved on specimens with the upper 



