330 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES 



Vauikoro ambigna, M. & H. 



Plate 19, figs. 12, a, b, c, d. 



Katica^ ambigua. Meek and Harden (185(5), Proceed. Acad. Nat. Sci. Philad., VIII, 64. 



Fossar? Nebrascensis, Meek and Hayden (1860), ib., XII, 4"23. 



Vanikoro ambigua, Meek (1864), Smithsonian Check-List N. Am. Cret. Fossils, 18. 



Shell rather small, obliquely rhombic-subglobose ; spire of moderate 

 height, composed of about four convex volutions, which are separated by 

 a well-defined suture; surface ornamented by distinct lines and obscure 

 wrinkles of growth, which are crossed by numerous irregular revolving lines, 

 generally larger than the grooves between ; aperture ovate, very oblique, 

 obtusely angular above, and rounded below; outer lip sharp, joining the 

 whorl above nearly at right angles, slightly reflexed at its junction with the 

 columella below; axis apparently perforated by a very small umbilical 

 opening, which is not covered by the lip. 



Length, about 56 inch ; breadth, 0.48 inch ; length of aperture, 36 

 inch ; breadth of same, 0.25 inch. Apical angle regular, or nearly so ; 

 divergence varying from 70° to 80°. 



The revolving lines are generally quite well defined, especially on the 

 lower part of the body-whorl. They are very irregular in size, though 

 almost always broader, particularly on the middle of the body-volution, than 

 the grooves between, which are each sometimes occupied by a smaller line. 

 By the aid of a lens, faint indications of very fine, revolving, impressed striae 

 may be seen irregularly distributed upon and between the larger lines. 



In form, this shell varies somewhat; the spire of some individuals being 

 more elevated than that of others. Some specimens have the body-whorl 

 rounded and rather gibbous, while in others it is slightly compressed above, 

 so as to give the shell a more conical form. 



In first indicating this species, we were in much doubt in regard to its 

 generic relations, and placed it provisionally, with a query, in the genus 

 Natica. Later comparisons, however, soon led to the conclusion that it at least 

 could not be properly retained in that genus, and we afterward removed it, 

 still doubtfully, to the genus Fossar. In making this change, it also became 

 necessary to find a new specific name, then; being already a Fossar anMguus. 

 Still more recently, some specimens were brought in showing more clearly 

 the parts about the columella and umbilical region, and from these it appeared 

 much more probable that this shell belongs to the genus Vanikoro, to which 



