INVERTEBRATE PALAEONTOLOGY. 331 



J removed it in the .Smithsonian. Check-List, under the original specific name. 



It is one of those puzzling types, such as the palaeontologist not unfrequently 



has to dispose of in some way, without being entirely satisfied with any 



conclusion that he can form in regard to its relations. 



Locality and position — Yellowstone River, 150 miles above its mouth; 



in the beds containing a mingling of the fossils of the upper part of the Fort 



Pierre group with those of the Fox Hills group, of the Upper Mo. Cretaceous 



series. 



Genus VANIKOROPSIS, Meek. 



Syvon.—Natica and Xeritopsis ? (sp.), Meek and Hayden (neither Nntica, Ad., nor Neritopsis, Grate].). 



Etym. — Vanikoro ; orpic, form. 



Type. — Nalica Tuomeyana, Meek and Hayden. 



Shell subglobose, thick, and solid; body-volution large; spire depressed; 

 aperture ovate; axis imperforated ; outer lip simple, beveled ; inner lip closely 

 folded upon, and adhering to, the columella and the body-volution, very little 

 thickened, and not flattened, toothed, notched, or serrated; surface with 

 distinct revolving lines and furrows, and on the body-volution developing 

 strong oblique folds or plications and furrows, parallel to the lines of growth. 



The type and only known species of this genus has long been a subject 

 of much doubt and perplexity. In first indicating it, we placed it temporarily 

 in the genus Natica, with really very little idea that it properly belonged 

 there. Subsequently, we removed if, with a mark of doubt, as a nearer 

 approximation to its true position, to the genus Neritopsis. In general form, 

 and the possession of distinct revolving lines and furrows, it reminds one 

 of the genus Vanikoro; but its very thick, solid shell, want of an umbilical 

 perforation, and the close connection of the slightly-thickened inner lip with 

 the columella and the body-volution above, forbid its reference to that group. 

 On the other hand, it presents quite as well-marked distinctions from Neri- 

 topsis, since its inner lip wants the thickened and flattened character of that 

 genus, and shows not the slightest tendency to the formation of a broad 

 central notch, or sinus, such as we see in the same. 



In regard to its geological range, nothing can be said, in the present state 

 of our knowledge, beyond the fact that the typical species came from the 

 higher part of the Upper Cretaceous. 



It is difficult to decide respecting the family -affinities of such a fossil 

 shell without, so far as known, any existing congeneric representatives. I 

 have the impression, however, that it may find a place in thefamily VanikorulcB. 



