1024 THE PALEONTOLOGY OP MINNESOTA. 



LEuomphalldai'. 



whorls, rounded or obtusely angular upon the upper side, the angle marking the 

 bottom of a broad sinus in the lip; the first departure from this type consisted in the 

 loosening and straightening of the last whorl (Eccyliomphalus, or as Whitfield would 

 have it, Caularops canadensis Bill, sp.); next all the volutions became~_disjoined as in 

 EC. intortus and the later EC. undulatus. We have no evidence to show that one or 

 the other of these stages was not strictly maintained as a specific peculiarity by 

 each of the early forms it certainly was so with the Trenton species but, accord- 

 ing to Lindstrom, the whorls in his E. gotlandicus vary from closely coiled to perfectly 

 evolute. All these species have a broad sinus in the upper lip and, so far as traced, 

 we have found no evidence to show that the later (Devonian and Carboniferous) 

 shells commonly referred to Straparollus (i. e. euomphaloid shells having rounded 

 whorls and nearly or quite straight transverse lines of growth) were developed from 

 them. On the contrary Straparollus or Straparollus-like shells seem to us to have 

 been evolved probably at several successive times from true Euomphali. Still, we 

 are not prepared to say that some of them may not have been derived from the 

 Lower Silurian species which Billings called Straparollina. However, though with 

 nothing but Billings' figures to base our judgment upon, we are strongly inclined to 

 regard Straparollina as closely related to Holopea and consequently as widely distinct 

 from the Euomphalidce. 



In our opinion, therefore, Eccyliomphalus, as this genus is defined and used by 

 most American authors, deserves recognition as a well-marked and limited generic 

 group, principally because it represents a distinct line of development. Phanerotinus 

 Sowerby, which is .similar in habit and sometimes considered as synonymous, is 

 founded upon evolute Straparollus-Euomphali of the Devonian and Carboniferous 

 rocks. As now used the genus is not a natural group, but it may well be retained, 

 provisionally at least, as a designation of convenience for those Euomphali having 

 rounded and more or less widely disjoined volutions and no apertural sinus. In 

 America only three species fulfill these requirements, viz.: P.parodoxus Winchell 

 (Burlington group), and P. eboracensis (Hamilton group), and P. laxus (Corniferous 

 group) of Hall. The second is peculiar because its shell attaches to itself foreign 

 objects. Eccyliomphalus undulatus Hall had a similar habit, and its frequent 

 occurrence in several European Devonian Euomphalidce has been observed by 

 Deslongchamps, Koken and others, and quite recently has led Kayser to propose the 

 new generic term Philoxene (Zeitschr. d. deutsch. geol. Gesellsch., Jahrg. 1889.) 

 This peculiar feature reminds one of the recent genus Phorus, but we agree fully 

 with Hall and Koken in attaching very little significance to its presence in these 

 otherwise clearly Euomphaloid shells. 



As far as we can go back in geological history, the developmental line of 



