910 THE PALEONTOLOGY OF MINNESOTA. 



LConradella bellula. 



We have two specimens of a variety or a closely related species from the Tren- 

 ton of Minnesota which we propose provisionally to designate as 



Variety CELLULOSA, n. var. 



PLATE LXVII, FIGS. 27-29. 



They are both only about 9 mm. in diameter, and differ from the typical form of 

 the species in having much less of a keel and in the peculiar modification of the 

 surface markings. The lamellae, namely, generally unite with each other in such a 

 manner that a cellular rather than striated surface results. When slightly weathered 

 the connected sides of the successive loops may appear like delicate longitudinal plates. 

 It seems to be a rule that the loops are oblique and joined to each other only on one 

 side, the other being open. Again it may appear that the longitudinal line is 

 independent and runs directly through the loops. The transverse lamellae are 

 unusually crowded, the average on the last volution being from eight to ten in 

 2 mm. 



The surface markings of C. dyeri have never been correctly illustrated. On the 

 accompanying plates we show that the " revolving ridges " are as a rule not ridges 

 at all, but only an appearance due to the elevation and longitudinal arrangement 

 of the closely following loops of the transverse lamellae. When continuous revolving 

 lines are formed it is only through coalescence of one or both sides of the loops of 

 succeeding lamellae. 



Compared with the preceding species C. dyeri is distinguished at once by its 

 smaller size and unusually crowded surface markings. 



Formation and locality. The typical form occurs in the Richmond group at Richmond and Versailles, 

 Indiana; Oxford, Clarksville, Freeport and Waynesville, Ohio; near Maysville, Kentucky, and Spring 

 Valley, Minnesota. Variety cellulom was found in the Clitambonites bed of the Trenton group at St. 

 Paul and Cannon Falls, Minnesota. 



Collection.-*!. O. Ulrlch. 



CONEADELLA BELLULA, n. Sp. (Ulrich.) 

 PLATE LXVII. FIGS. 23-26. ^ 



This species in most respects occupies an intermediate position between C. dyeri 

 Hall and C. elegans Miller. From the former it is distinguished by its lesser 

 thickness (compare figures 24 and 31 on plate LXVII) less crowded lamella, and by 

 having numerous well marked lunulae on the slit-band. From C. elegans it differs in 

 having more slender whorls and less coarsely marked surface. 



