WHITB.J PALEONTOLOGY — CRETACEOUS FOSSILS. 313 



cupying only about one-third of the full length of the outer lip^ blunt 

 or abruptly rouuded at the posterior end of the posterior projection, in- 

 stead of being falciform, as is usual in this genus ; outer lip, exclusive of 

 the wing lu'oper, moderately broad, prominent, sloping fi^om the i)osterior 

 base of the wing to the last suture, Avith a gently convex border, sloping 

 with a very gently sinuous border from the anterior base of the -wing to 

 the pointed front of the shell ; inner hp having a moderately broad, dis- 

 tinct callus, extending from the anterior end of the columella to or nearly 

 to the last suture; aperture elongate, narrow. Volutions of the spire 

 marked by many longitudinal folds, which are somewhat more oblique 

 upon the smaller volutions than upon the larger, and extend almost or 

 quite to the suture upon both the proximal and distal side of the volution. 

 These folds are continued upon the body- volution, but are not extended 

 upon its anterior half, and give place to smaller, iiregidar wrinkles ui)on 

 approaching the outer lip. These wrinkles are smaller at the base of 

 the wing, but upon, the outer recurved x^ortion they become conspicu- 

 ously strong. The whole surface is marked by iine revolving, raised 

 striiie, which, with the Hues of growth, produce a more or less distinctly 

 cancellated appearance. No true angulation or carination of either the 

 volutions or the wing exists. 



Length from the pointed front to the apex of the spire, about 29 milli- 

 meters ; breadth across the body-volution, including the wing, 20 milU- 

 meters ; breadth of the body- volution, from the callus of the inner Uj) to 

 the outer surface, 9^ millimeters. 



Few famiUes of shells present greater difficulties in the way of a rea- 

 sonably precise diagnosis of the genera which compose it than the Apor- 

 rhaidccy an exemphtication of which fact is afforded by the four species 

 embraced in this paper. Possibly the species here described ought to 

 be ranged under Arrlioges Gabb, as a subgenus of Aporrhais ; but it 

 has no posterior canal, and the only feature by which it materially dif- 

 ers from Drepanocheilus Meek is the blunt instead of pointed i)Osterior 

 extension of the wing, and the absence of a carina or any angulation 

 of its dorsal surface. This peculiarity of the wing, indeed, distinguishes 

 it from any i)ublished species of the section of the family to which it 

 belongs. 



Position and locality. — Cretaceous strata; Denison, Tex., where it was 

 collected by Prof. B. F. Mudge, and in whose honor the specific name is 

 given. 



Anchuka (Drepajstgcheilus) pkolablata \Vhite. 



Plate 7, fig. 2 a. 

 Anchura prolaiiata White, 1876, Powell's Eep. Oeol. Uinta Mts. p. 121. 



Shell rather above medirnn size, subfusiform; spire elongated and 

 tapering to a point, with nearly straight sides ; volutions nine or ten, 

 convex, the last one proportionally a little more enlarged than the others, 

 the distal margin of each narrowly appressed against the proximal side 

 of the next preceding one at the sutiu'e ; wing large, broad, its outer 

 border nearly straight or slightly convex, its anterior extremity abruptly 

 rounded to the broadly concave front margin ; posteriorly the wing is 

 divided into two somewhat broad, prominent, blunt processes du-ected 

 backward and a little outward, the inner one of the two being the nar- 

 rower, and occupying a position about midway between the spire and 

 the extreme outer margin of the wing ; posterior border of the wing con- 

 cave between the spire and the extremity of the first i)rocess, and less 



