144 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bttll.100. 



Aporrhais (Perissoptera?) prolabiata White (sp.) 



PI. xxxi, Fig. 2. 



Anchura prolabiata White, 1876, Geol. Uinta Mts., p. 121. 



Anchura {Drepanocheilus) prolabiata White, 1879, Ann. Rept. U. S. Geol. Sur. Torr. for 



1877, p. 313, PI. 7, Fig. 2a. 

 Compare Anchura f fusiformis White, 1876, U. S. Goog. and Geol. Sur. West 100th 



Meridian, vol. IV, p. 190, PI. 18, Fig. 4a. 



The following is Dr. White's description, with a few changes and 

 corrections made necessary by the better material now before me: 



Shell rather above medium 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 suture; wing large, broad, its outer 

 border, nearly straight or slightly con vex, its anterior extremity abruptly 

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

 divided by a deep rounded sinus into two portions, the posterior of 

 which is narrow and directed backward and a little outward in a slender 

 pointed process, while the anterior portion is larger and subquadrate, 

 with the outer angles slightly produced. Anterior canal and beak 

 short; no posterior canal, though the outer lip is slightly produced 

 backward and attached to the penultimate volution ; inner lip and adja- 

 cent parts of the shell glazed, but without a distinctly marked callus. 



Transverse costae slightly curved, scarcely half as wide as the inter- 

 spaces, usually well marked on the whole spire, and gradually increas- 

 ing in prominence on each succeeding whorl until on the back of the 

 body volution they become narrow elevated ridges that extend from 

 the suture to about the middle of the whorl, but on a few specimens, 

 such as the original type, the transverse ornamentation is less prominent 

 throughout and almost obsolete on the body whorl, and it is always 

 more or less indistinct for some distance around the inner lip. In 

 addition to these regular costie the spire sometimes bears a number of 

 heavy varices that are not quite parallel with them. The entire surface 

 is covered with crowded revolving raised lines that are barely visible 

 without the aid of a lens. There is no carina on the body volution, but 

 the posterior process of the wing is subcarinate, especially toward the 

 extremity. 



Length of the largest specimen, 47 mm ; breadth, across the wing and 

 body volution, 34 m,T1 ; diameter of the body volution, 18 mm . 



No closely related species has been described from the American 

 Cretaceous, though Bostellaria rostrata Morton, a Kipley species, 

 should probably be referred to the same section. In the Cretaceous of 

 Europe there are many similar forms, such as Aporrhais parJcinsoni, A. 

 reussi, A. schlotheimi, etc., ranging from the Gault to the lower Senonian, 

 inclusive. 



