staoton.] NATICID^, RISSOIDiE. 139 



Genus SIGARETUS Lamarck. 



SlGARETUS (EUNATICINA?) TEXTILIS n. Sp. 



PI. xxx, Figs. 5 and 6. 



Shell thin, broadly ovate, consisting of three or three and a half rap- 

 idly increasing volutions, the last one forming the greater part of the 

 entire bulk; suture linear, impressed; aperture large, rhombic ovate, 

 narrow and produced behind, broad and sinuous in front, the greatest 

 breadth being in front of the middle; outer lip thin and sharp, irregu- 

 larly convex in outline; inner lip somewhat thickened and reflected, 

 almost covering the narrow umbilical chink; columella arched. The 

 inner lip is also concave in the middle, so that it and the narrow 

 umbilicus are concealed when the aperture is filled with rock. 



Surface marked by distinct revolving filiform lines that are not quite 

 a millimeter apart on the body whorl, and by crowded, wavy trans- 

 verse lines that are just visible to the unaided eye. On several of the 

 specimens the revolving sculpture is very faint on an area of 2 or 3 mm 

 wide bordering the outer lip, and the lines of growth are there more 

 distinct. 



Length of the largest type, 15 mm ; breadth, 12 mm . 



The generic relations of this species are rather obscure, and the 

 specimens in hand are not very well preserved. Mr. Charles T. Simp- 

 son, of the department of mollusks, U. S. National Museum, through 

 whose courtesy I was enabled to make comparisons with recent species, 

 decides that it is most nearly related to Sigaretus and to the subgenus 

 Eunaticina of Fischer {—Naticina Gray). 



Naticina obliqua Gabb, from the Tejon formation of California, is the 

 only other American species that has been referred to the Cretaceous, 

 and it is plainly different from ours. 



Locality and position. — Upper Kanab valley, Utah, about 300 feet 

 above the base of the Cretaceous section. 



RISSOID^E. 



Genus MESOSTOMA Deshayes. 



Mesostoma occidentalis n. sp. 



PI. xxx, Figs. 7 and 8. 



Shell scalariform, with about eight or nine convex whorls; sutures 

 deeply impressed. Surface marked by numerous moderately strong 

 transverse costae, that pass entirely across the whorl and are about as 

 broad as the interspaces, and by more closely arranged, fine, revolving 

 lines. On each of the larger whorls there are about twenty of the 

 transverse costae and about twelve or fifteen revolving lines. 



