I'ol'A 

 Trtroul turner. 1 



ami wi.lth UMIU- -ively as two is to five. The dorsal ridges differ in this that 



the cent m-lateral pair continue- in full strength almost or quite to the apertural 

 margin. There i- U-M.les a lateral pair of ridges, not so strong as the others though 

 still .|mte -li-fiiict. making in all six revolving ridges. This outermost pair may 

 occasionally appear to be represented in '/'. /WK/-M//.I. though never so distinctly; 

 yet when carefully compared it will he noticed that T. sercarinaia really has an 

 extra pair. -ince the ones which in Hall's species form the extreme lateral bound- 

 aries of the volutions, ami at the same time the edge of the umbilicus, are present 

 also in T. tej-oiritmtn. The umbilicus is of about the same size and character in the 

 t\v species. Imt the mouth and surface markings are different. The sinus in the 

 outer lip, namely, is deeper and much wider, the backward sweep of the lines of 

 growth beginning already between the edge of the umbilicus and the outer ridge 

 instead of at the centro-lateral ridge. Furthermore, the lines are much farther 

 apart and coarser, the distance from line to line averaging about 1 mm. Finally, 

 the lines of growth are, though more or less obscurely, reproduced on casts of the 

 interior, while no trace of them is observable on casts of the other species. 



With the differences mentioned there can be no reasonable doubt about the 

 specific distinctness of T. sexcarinnfn and T. l>iilnrxntn\ and the others are still farther 

 removed. Good adult specimens cannot be confused, only the young being 

 sufficiently alike to render separation difficult. 



Formation and locality. Stoat* Kiv.-r trroup (Vanuxemla bed), Minneapolis, St. Paul and Cannon 

 Palls. Minnesota: Beloitand Jan. ^ ill.-. Wis.-..n*in: ln\.,n. III.; Lebanon and Lavergne, Tennessee. Tren- 

 ton gruup (Fuslsplra bed), Kf Union- county, Minnesota. 



O9Bert4<MM.-Geologlcal and Natural History Survey of Mlnneaota; E. O. Ulrlch. 

 IftUMm Krgutr, Nos. 6064, 7530. 



TKTRANOTA MACKA. n. sp. 



ri l IU3. i and t. 



This species remiml- one in its marking* of '/'. sexcarinata, but has only four 

 dorsal ridges. The lines of growth also are stronger, showing distinctly on caste. 

 The umbilicus is relatively larger than in any of the other species of the genus and 

 the sides of the volutions more -harply angular. Corresponding differences occur 

 in the form of the aperture. 



Formation and healitf. Vanuxemla bed, Stones Rlv.-r k'roup, Minneapolis, Minnesota. 

 .-E.<> Ulrlch. 



