INVERTEBRATE PALAEONTOLOGY. 335 



2; ALABA, IT. mid A. Adams. 



Shell smooth, or sometimes with a few irregular varices, semi- 

 pellucid ; aperture only slightly emarginate. — (C. melanura, 0. B. Ad.) 

 3. seila, A. Adams. 



Shell differing from other species of the genus in being trans- 

 versely Urate, instead of ribbed, granular, or cancellated. — (Triphorii 

 dext rover sus, Adams and Reeve.) 



Although the little, shells included in this genus so nearly resemble 

 those of Cerithium that it is exceedingly difficult to distinguish the two groups 

 from each other, when the soft parts are unknown, the animal of Cerithiopsis 

 is so peculiar that an entirely distinct family has been established for the 

 reception of the genus. 



Although I have not very much faith in the possibility of distinguishing 

 this genus from Cerithium among fossil species, as I have already referred to 

 it elsewhere one of our Upper Missouri Cretrceons species that certainly 

 resembles some of the recent species of this group in size and form, as well 

 as in the nature of its aperture, I do not like to remove it to Cerithium on 

 uncertainties, and therefore have had to characterize the genus here. 



The difficulty of distinguishing this genus from Cerithium, of course, 

 precludes the possibility of fixing or determining its geological range with 

 precision. There are certainly, however, forms in the Cretaceous rocks that 

 seem to present all of its characters, so far as the shell can be relied upon as 

 a guide ; also in the Tertiary. It is likewise moderately well represented in 

 our existing seas. 



Cerithiopsis Moreauensis, M. & H 



Plate 31, fig. 4 (not 4 a b). 



Titrritella Moreauensis, Meek aud Haydeu (1856), Proceed. Acad. Nat. Sci. Pbilad., VIII, 70. 

 Cerithiopsis Moreauensis, Meek and Hayden (1860), ib., 185. — Meek (1864), Smithsonian Check-List N. Am. 

 Cret. Fossils, 20. 



Shell small terete ; volutions flattened on a line with the general slope 

 of the spire, increasing gradually and regularly in size from the apex, and all 

 without traces of varices ; last one nearly rectangular around the lower 

 margin, each turn bearing three continuous, prominent, revolving lines, or 

 little ridges, separated by furrows of the same, or very slightly larger size; 

 suture appearing like a mere impressed hair-line, in a spiral furrow between 



