1050 THE PALEONTOLOGY OF MINNESOTA. 



(Trochonema bellulum. 



triangular than quadrangular in a ventral view though decidedly quadrangular in a basal view. The 

 inner and lower lips also are more strongly reflected and thicker than in any other species of the genus 

 known. And yet, the shell is not much thicker than in T. umbilicatum. 



Formation and locality. Upper division ("Glade limestone") of the Stones River group, near Leba- 

 non, Tennessee. 



Collections. Prof. J. M. Safford; E. O. Ulrich. 



TROCHONEMA BELLULUM, n. sp. (Ulrich.) 



PLATE LXXVII, FIGS. 26-29. 



At first we were inclined to unite this species with T. eccentricum, but a more careful comparison 

 revealed differences of sufficient importance to deserve recognition. In the first place the adult shell is 

 much smaller, the width of the largest specimens being less than 25 mm. (in five out of six it is less than 

 20 mm.), while it is from 35 to 40 mm. in adult shells of 1. eccentricum. Next, the apical angle is usually a 

 trifle narrower, giving a proportionally higher spire. Finally, the lines of growth are finer and turn 

 slightly forward instead of backward in crossing the concave peripheral space, thereby producing, with 

 the retrally curved striae of the upper side, a slight notch at the upper peripheral carina. Such a wide- 

 angled notch occurs in three other species, viz.: T. retrorsum, T. subcrassum and T. madisonense of this 

 report, but they are all readily distinguished from the present species by other characters. Compared 

 with T. umbilicatum, T. fragile and other similar species, T. bellulum is distinguished at once by the 

 eccentric sweep of the umbilical ridge and the subtriaogular shape of the aperture resulting from it. 



Formation and locality. Lower division ot the Stones Eiver group, Murfreesboro, Tennessee. 

 Colkctions. Prof. J. M. Safford; E. O. Ulrich. 



TROCHONEMA FRAGILE, n. sp. 



PLATE LXXVII, FIGS. 1316. 



This is a small form, the greatest diameter averaging about 15 mm., the largest seen being only 

 about 22 mm. wide. The specimens closely resemble young testiferous examples of T. umbilicatum, but it 

 is to be noted that It is the internal cast that agrees in its general appearance with the exterior of that 

 shell. We have not seen the exterior of T.fragik, but the unusual sharpness of the angles indicates a 

 very thin fragile shell, probably similar, even to the surface markings, remains of very delicate equal 

 lines of growth being retained by one of the specimens, to the variety of T. umbilicatum which we 

 distinguish as var. canadense. The lower or umbilical side must be almost exactly as in that variety, but, 

 judging from the differences exhibited between the interior and exterior of other species of the genus, the 

 lower boundary of the vertical peripheral face must be even more prominent than in var. canadense. 

 Further comparison brings to light another difference that we believe will serve to separate the species at 

 all times from that variety. Namely, the uppermost of the four carinae is proportionally much nearer the 

 suture in T.fragik, being removed from it but little more than one-fifth of the width of the upper surface 

 of the whorl, whereas in all the varieties of T. umbilicatum the distance equals at least a third. In this 

 feature the spec! s agrees with T. subcrassum and T. retrorsum, which see for comparisons. It is scarcely 

 possible that T. fragile can be confounded with any of the other species here described. 



.Formation and locality. Clitambonites and Fusispira beds of the Trenton group at various localities 

 in Goodhue county, Minnesota. Also in beds equivalent to the latter horizon in Carroll county, Illinois. 



Collections. Geological and Natural History Survey of Minnesota (2 specimens); W. H. Scofleld (3 

 specimens); E. O. Ulrich (7 specimens). 

 Museum Register, No. 8735. 



