954 THE PALEONTOLOGY OF MINNESOTA. 



[Synopsis of Pleurotomariidoe. 



they pass almost directly across the whorl, a short backward curve occurring only 

 just before they reach the periphery. Types, PI. etna and ramsayi Billings. 



At least two other species, the PI. amphitrite Billings and PI. beekmanensis 

 Whitfield, are known to belong to this generic type. A possible fifth species (it may 

 be the same as Billings' etna) occurs at Ft. Cassin, Vermont. With the exception of 

 the species amphitrite, which may be a Chazy fossil, all these forms occur in the 

 Calciferous formation, so that the genus represents one of the earliest fixed types of 

 the family. Though fixed, in the sense that the known species adhere very strictly 

 to the characters mentioned in the generic diagnosis, the type was evidently of 

 vShort duration. We have very carefully examined the Pleurotomariidce found in 

 succeeding geological divisions but have failed entirely to discover any that might 

 reasonably be viewed as descendants of Euconia; nor do we know anything positive 

 about their ancestors. We are therefore obliged to consider the genus as a 

 rapidly evolved, short and abruptly terminated branch from the stock which 

 produced also Liospira on the one side and Eotomaria on the other. Euconia is 

 distinguished from all of the Lower Silurian Pleurotomariidce by the regularly 

 conical spire and flat base, and the very slight curvature of the lines of growth on 

 the under side of the whorls. These features are all reproduced in the Carboniferous 

 group of shells which we propose to distinguish as Euconospira, but they have 

 another character, namely, a long open slit, which is absent in Euconia and of itselt 

 demands a separation. The surface of the Carboniferous shells differs also in being 

 spirally lined. 



VII. EOTOMARIA, n. gen. Shell depressed-conical, sometimes sublenticular; 

 base more or less convex, its bulk usually neai'ly equal to the apical part; umbilicus 

 very small or wanting; volutions not very numerous, sometimes slightly turriculate 

 or strongly angular near the mid-hight; aperture oblique, subquadrate, the inner lip 

 slightly reflected or merely thickened, the outer deeply notched at the peripheral 

 angle; no slit; band of moderate width, concave, sharply defined, oblique or 

 horizontal, lying upon the apical side of the periphery. The surface markings 

 consist of fine lines of growth only. These curve backward more or less strongly 

 toward the band on both the upper and lower sides of the whorls. Type, E. sublcevis, 

 n. sp. (Ulrich.) 



VIII. CLATHROSPIRA, n. gen. Shell in all respects like Eotomaria except that 

 the band is nearly vertical and situated upon the periphery of the whorls, and the 

 surface beautifully cancellated. Type, PI. subconica Hall. 



IX. BEMBEXIA, (Ehlert, 1887.* Shell depressed subconical, imperforate, volu- 

 tions angular; band distinct, concave, vertical or oblique, situated on the periphery, 



EXIT. Bull. Soc. d'Etu. Sclentlf. d' Angers.p.'St. 



