128 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull.106. 



two species as above described, it was soon evident that they could not 

 be separated by form alone because they vary in that respect, showing 

 every gradation between the extremes represented by the types. The 

 type of JV. pisum was then studied more closely, and the rock was 

 removed from the aperture, revealing the fact that the inner lip is den- 

 ticulate as in N.pisiformis. Consequently the latter name must be re- 

 garded as a synonym of 1ST. pisum. 



Locality and position. — Near the base of the Cretaceous section at 

 Coalville, Utah. 



Neritina incompta White. 

 PI. xxviii, Figs. 4 and 5. 



Neritina incompta White, 1879, Ann. Rept. U. S. Geol. Sur. Terr, for 1877, p. 308, PI. 

 7, Figs. a-c. 



Original description: 



" Shell transversely elongate when adult; spire depressed, abruptly 

 convex, small, but rising perceptibly above the body- volution ; volu- 

 tions three and a half or four, increasing rapidly in size, the last one 

 comprising much the greater part of the shell, regularly convex or with 

 a faint appearance of flattening upon the distal side of the last one; 

 suture moderately distinct; aperture rather large, its outer border reg- 

 ularly ro'unded, proximal, and distal margins slightly convex and sub- 

 parallel; outer lip thin-edged, inner lip moderately long, plain, slightly 

 concave upon its face, not very broad, sloping inward. Surface marked 

 by ordinary lines of growth. 



" Length, in direction of the axis, 12 mm ; breadth, across the aperture 

 and body- volution, 17 mm . 



" This species resembles N~. bannister i Meek from the brackish- water 

 layers of the same formation at Coalville, Utah ; but it differs in the 

 greater, although slight, elevation of the apex, the nearly straight, 

 instead of curved, border of the inner lip, and its nonpolished surface." 



Locality and position. — Valley of Sulphur creek, near Hilliard sta- 

 tion, Wyoming, in strata that are now believed to belong to the Colo- 

 rado formation. 



.Neritina (Yelatella) patelliformis Meek. 



PI. xxviii, Figs. 6-10. 



Nerltina (Dostia ?) patelliformis Meek, 1873, Ann. Rept. U. S. Geol. Sur. Terr, for 1872, 



p. 498. 

 f Neritina ( Velatella) carditoides White, 1876, U. S. Geog. and Geol. Sur. West 100th 



Meridian, vol. iv, p. 189, PI. 18, Fig. la-c. 

 Neritina ( Velatella) patelliformisWhite, 1879, Ann. Rept. U. S. Geol. Sur. Terr, for 1877, 



p. 309, PL 7, Figs. la-d. 

 Neritina ( Velatella) patelliformis var. weberensis White, 1879, ibid. PI. 7, Figs. 8a and b. 



Original description. 



"Shell small, thick, oval, or subellipticj nucleus nearly posterior 

 and generally more or less elevated above the posterior margin, but 



