1058 THE PALEONTOLOGY OF MINNESOTA. 



[Oyclemrna blllx. 



cancellatum Lindstrom (not Hall's sp.), to Strophostylus as here understood. We have 

 not had an opportunity to examine any of the Devonian species that are referred to 

 Cyclonema by various authors, but judging from the literature alone we feel satisfied 

 that not one has a sufficient right to maintain its position in the genus. Lindstom's 

 description of Cyclonema is incorrect since it is based principally or solely upon the 

 Gotlandic species described by him. He places the genus into the immediate 

 vicinity of Polytropis (Oriostoma) because he has found an operculum similar to the 

 type prevailing in that genus in Hisinger's* Turbo striatus which he places, together 

 with several similar and other very different shells from Gotland, under Cyclonema. 

 Though we have collected thousands of specimens of typical species of Cyclonema, 

 not a single operculum of any kind has ever occurred in connection with them. We 

 conclude, therefore, that Cyclonema had no operculum, at any rate none that could be 

 preserved as a fossil. 



CYCLONEMA BILIX Conrad. 



PLATE LXXVIII. PIGS. 35-42. 



Pleurotomaria bilix CONRAD, 1842, Jour. Acad. Nat. Sci. Phila., vol. viii, p. 271; (part.) HALL, 1847, 



Pal. N. Y., vol. 1, p. 305. 



Cyclonemu bilix HALL, 1852, Pal. N. Y., vol. li, p. 89. 

 Cyclonema bilix (part.) HALL, MEEK, MILLER, and others. 



Shell subconical, the hight and width equal, or the night may exceed the width by as much as one- 

 fifth or in rare cases even one-fourth; apical angle varying from 55 to 75. Whorls generally three or four 

 in number, the nucleus, consisting of three more, being absent in nearly every instance. In the typical 

 form the whorls are depressed convex, flat or even a trifle concave in the central part of the exposed slope 

 while at the top there is nearly always a small shoulder-like convexity which, with a similar convexity at 

 the bottom, produces a distinctly impressed suture. Base of body whorl more or less flattened, narrowly 

 rounded at the periphery; no umbilicus. Aperture oblique, somewhat triangular in a view of the base- 

 subquadrate in a ventral view, the upper and inner sides of about the same length, and each about two, 

 thirds as long as the lower side, while the outer side equals in length both the inner and upper sides; inner 

 lip excavated, the excavated portion narrowly crescentic in shape, gently concave or straight on the inner 

 side and strongly convex on the outer, usually 1.5 mm. across its widest part, rarely 2.0 mm. or more in old 

 shells; inner margin of excavation sharp below, becoming more and more rounded toward the upper 

 extremity where it turns sharply into the mouth. Surface marked by numerous, small, more or less reg- 

 ular revolving ridges and by much finer, sharply elevated, lines crossing the whorls from above obliquely 

 downward and backward. On the outer surface of the upper whorls the revolving lines are mostly of the 

 same size with from nine to twelve on each. On the body whorl where a new set is interpolated they gen- 

 erally alternate in size, with an average of ten or eleven in 5 mm. Of the oblique transverse lines, which 

 run parallel with the margin of the aperture and are more closely arranged in this species than usual for 

 the genus, the number in 5 mm. on the last whorl averages about thirty but varies between the extremes 

 of twenty-five and forty. The last whorl of old examples usually exhibits more or less numerous irregula 

 undulations and wrinkles of growth which generally cause some irregularity in the surface orna 

 mentation. 



The hlght of specimens usually varies between 15 and 20 mm.; occasionally it may reach 30 mm. 



We could not satisfy ourselves that Cyclonema fluctuatum James is more than a good variety of C. 

 bilix. Mr. James included in his species some specimens that do not deserve to be distinguished even as a 

 variety, but we believe the majority of his types are of an abundant variety that is generally quite easily 



