GASTROPODA. 



!'!. utaliois niii-ii thi'-k-r. the urfa<v markings coarser, the angles more proiiiiii.-ni. ami ti.. uuil.il- 



: .1*1 whorl often show* a tendency to iH-nmie disjoined, but tin- r.-.iiur.- Is ti. 

 I a. In our T. rayram. Casts of tin- m!.-:i..r. because "f tin- thick -h.-ll. have uniiHiially rounded 

 h..rN, ami (hew are even mure readily distinguished from T. umMicatum than an* the shells. Tin- U|>|><T 

 . u. .ii.-r i: < -.inn .1- li always* clearly Indicated by a mumled rlilf with minor n-volvlnjj undula- 



.v* ttu.wn In ..iir tl*. 3. The lower carlna, however, semi always to be but obscurely reproduced on 

 cants. Th.- iiinlilllcal rldire. on the other hand, Is more distinct on casts than on the shell lUelf. As may 

 be seen In Og. 4, It becomes quite obsolete with age. In the Minnesota form of ih<> species the whorls 

 seem always to be more slender than In specimens from Wisconsin. 



and locatoy.- Stones River group, Minneapolis and St. Paul. Minnesota; Mineral Point 

 and Itelult. Wisconsin, and Dlxon, Illinois. 



CbUMtoik-E. O. Ulrlch. 



TROCIIONEMA VAORANS, n. sp. 



ri.ATK I.\\VII HO. 46; PLATE LXXMII. HOS. 10-U. 



This form is closely related to T. beloiunie perhaps merely a variety of that species. It has more 

 slender volutions, a thinner shell and, considering the size of the specimens, stronger surface markings. 

 The shell being of only moderate thickness, the whorls of casts are also more angular. The last whorl Is 

 over half free and drops rapidly. 



Formation and locality. Stones River group, Vanuxemla bed, Minneapolis, Minnesota. Apparently 

 a rare fossil. 



CbUeetioiu. Geological and Natural History Survey of Minnesota; E. O. Ulrich. 

 Muteum Register, No. OM6. 



TROCHONEMA RUOOSUM, n. sp. 



PLATE LXXVII. FIOS. l-S. 



is of this species have a much smaller umbilical perforation than 7'. umlrilieutum. This Is due 

 chiefly to the much thicker shell, the size of the umbilicus In casts of the two species being more nearly 

 equal. For the same reason the mouth of T. rugonum, as seen on casts, appears to be abruptly expanded, 

 especially upon the lower and outer side). The upper side of the whorls (In casts) Is also more strongly 

 convex (not angular) In the Inner half and more deeply concave in the outer. On both the cast and shell 

 the two peripheral carlna- are more prominent, causing the space between to be more excavated. The 

 surface markings are very coarse, turned backward on the upper side of the whorls, vertical on the concave 

 peripheral face and again turned backward, though not as strongly as In T. umbUiratum, on the lower side. 

 Here, particularly toward the aperture of adult examples, the stria- are often more numerous, sometimes 

 two to one, than on the peripheral band. 



locality. Stones Ulver group, Vanuxemla bed, Minneapolis and St. Paul, Minnesota; 

 ilelolt. Wisconsin. 



CWtertioiu. Geological and Natural History Survey of Minnesota; E. O. Dlrlch. 



TROCBONKMA BCCBNTRICUM, n. sp. (Ulrich.) 



PLATE I.XXVIl. KI08. 17 and II. 



Young examples of this species must be almost lndi*Un k 'uNhable from T. umbUicatum. the general 

 aspect and surface markings being practically the same In both. Fully grown examples, however, are 

 separated at once by the bawl or umbilical ridge which, Instead of maintaining a subroedian posltl 

 swung outward gradually In the latter half of the last turo until It Is Immediately beneath the periphery. 

 This peculiarity results In well-marked differences In the shape of the mouth, the latter appearing more 



