180 GASTEEOPODS. 



expanded than the average specimen, while the spire is closely 

 incurved, even touching the body of the shell. When the gas- 

 teropod is found attached to strongly convex surfaces, or to 

 the calyces of Platycrinus, the shell enlarges less rapidly, and 

 there is also a tendency for the apex to become free from the 

 body-whorl, and even to completely uncoil, often to such an 

 extent as to approach closely some forms of the I. pabulocri- 

 nus type. 



Owen apparently had this form in hand when he figured a 

 shell as Ancella crasicollis from the Keokuk rapids of the Mis- 

 sissippi river, where it occurs quite abundantly. Its manner of 

 preservation, however, tends greatly to obscure its real char- 

 acter; and it is doubtless for this reason chiefly that Owen 

 failed to detect the true nature of the form. 



Capulus ovalis (STEVENS). 



Acroculia ovalis Stevens, 1858 : Am. Jour. Sci., (2), vol. XXV, p. 261. 

 Platyceras Icevigatum Meek & Worthen, 1866: Proc. Acad. Nat. Sci., 



Phila. , p. 263. (Not Acroculia Icevigata McCoy.) 

 Capulus ovalis Keyes, 1890: Proc. Acad. Nat. Sci., Phila. , p. 176. 



Shell very small, subglobose ; volutions about two and 

 one-half in number, contiguous, rather rapidly expanding ; spire 

 very small. 



Horizon and localities. Kaskaskia limestone : Union and 

 Eandolph counties, Illinois ; Ste. Genevieve county, Missouri. 



Capulus ovalis is one of the smallest of the lower Carboti- 

 ferous Capuli, having a height of only three to six millimeters 

 and a maximum breadth of eight millimeters. 



Capulus parvus SWALLOW. 

 Plate liv, figs. 5a-b. 



Capulus parvus Swallow, 1858 : Trans. St. Louis Acad. Sci.. vol. I, p. 205. 

 Platyceras nebrascense Meek , 1872: U. S. Geol. Sur. Nebraska, p. 227, pi. 



iv, fig. 15. 

 Platyceras nebrascense White, 1875: U. S. Geog. Sur. w. 100 merid., vol. 



IV, p. 159, pi. xii, fig. 5. 

 Platyceras nebrascense White, 1884 : Geol. Sur. Indiana, Kept, for 1883, p. . 



159, pi. xxxii, figs. 15 and 16. 



Capulus parvus Keyes, 1890: American Geologist, vol. VI, p. 9. 

 Capulus parvus Keyes, 1890: Proc. Acad. Nat. Sci., Phila., p. 178, pi. ii,. 



figs. 14a-c. 



