962 THE PALEONTOLOGY OF MINNESOTA. 



LLophospira. 



or greater differences in the bight of the spire are to be observed in the Perangulata 

 section. Beginning with forms like L. ampla Ulrich and L, multigruma Miller, in 

 which the apical angle varies from 70 to more than 90 degrees, we pass by numerous 

 and easy gradations to L. bowdeni Safford, in which the angle is sometimes as narrow 

 as 25 degrees. While the hight of the spire only rarely deserves to be counted among 

 the generic characters, we believe it is, within reasonable limits, usually an excellent 

 specific character. 



Concerning the systematic position of the genus, we may say with considerable 

 confidence that it is the oldest of the many types strictly belonging to the family 

 Pleurotomariidce. We say this not so much because the genus goes far back in 

 geological time, for, according to known facts, several other types are equally 

 ancient, but because it shares characters with types belonging to other families 

 which, like the Pleurotomariidce, originated somewhere in the interval between the 

 Calciferous and the Upper Cambrian. Thus the simplicity of the band and apertural 

 notch allies the genus with the Euomphalidce. A striking resemblance, indicating, 

 we believe, also close relationship, obtains between certain species of Trochonema 

 and Lophospira notabilis, L. knoxvillensis and L. trochonemoides. This relation of 

 Trochonema to the notched pleurotomarian and euomphalid genera is shown not 

 only by the species of Lophospira just mentioned, but is indicated quite as strongly 

 by such undeniable Trochonemas as T. retrorsa and T. bellula. The latter have an 

 apertural notch at the end of the supra-peripheral angle, causing the lines of growth 

 to curve backward toward the angle from both above and below. Only one feature 

 remains to distinguish the Trochonemoides section of Lophospira from T. retrorsa and 

 its allies, and that is, that while the Lophospiras have a distinct band, the Trochon- 

 emas have none, the lines of growth curving backward to and then over the angle 

 without interruption in the latter. 



Lophospira is divisible into four sections, and two of these into several subsections 

 as follows: 



A. Perangulata section: Apertural notch > shaped, deep and wide, the lines of 

 growth sweeping backward strongly from both above and below to the peripheral 

 band. 



1. Perangulata subsection: Shells not very high, whorls five to eight, strongly 

 angular. Species: L. perangulata Hall, L. sorocula Billings sp., L. modesta Billings 

 sp., L. medialis U. and S., L. decursa Ulr., L. pulchella U. and S., L. snffordi Ulr., 

 L. abnormis Ulr., L. centralis Ulr., L. oweni U. and S., L. ampla Ulr., L.peracuta U. and 

 S., L. elevata U. and S., L. multigruma Miller sp., L. tropidophora Meek sp., L. sumner- 



