1064 THE PALEONTOLOGY OF MINNESOTA. 



[Strophostylus textilis. 



principal reason for distinguishing the two groups of species lies in the conviction 

 that they represent two separate lines of development. 



Most authors place Strophostylus in the immediate vicinity of Platyceras and 

 Platystoma. In a measure this arrangement is quite correct, but Lindstrom surely 

 was not justified in reducing Strophostylus to synonomy under Platyceras. He quite 

 ignores the close relations of the genus to Cyclonema indeed it is evident that he did 

 not recognize the most essential feature of either Cyclonema or Strophostylus, since 

 he places at least one undeniable member of the present genus under Cyclonema. 

 ' We refer to his Cyclonema cancellatum. Even his C. delicatulum and C. adstrictum, 

 which do not belong to Cyclonema, may very well go under Strophostylus. 



STROPHOSTYLUS TEXTILIS, n. sp. 



PLATE LXXXII. PIGS. 49-54. 



Shell rather small, 12 to 25 mm. high, 11 to 20 mm. wide, obliquely conical; apical angle 60 to 70; 

 whorls, in casts, three or four, in entire shells, six or seven, increasing quite regularly in size from the 

 acute apex, almost uniformly rounded, often with several widely separated, deep, oblique constrictions; 

 suture deep; aperture subovate, oblique; inner lip appearing thin in a ventral view, but when a part of the 

 outer wall is removed it is seen that it forms a moderately thick columella with a spiral fold beginning near 

 the lower angle. In young examples neither the fold nor a spiral furrow just above it is very distinct, 

 while in some cases the whole inner lip appears to be simple and thin as in Holopea. Surface beautifully 

 cancellated by subequal, fine, sharp, revolving and obliquely transverse lines, the network growing strong 

 enough on the last whorl to be distinctly visible to the naked eye. 



This graceful and beautifully marked shell cannot be confused with any other known to us from the 

 Lower Silurian rocks of America. There are several Upper Silurian forms that resemble it, but in all of 

 these either the transverse or the revolving set of striaj is stronger than the other. Cyclonema graclk has 

 about the same shape, but its inner lip and surface markings are quite different. The apex also is different, 

 being conical in the Strophostylus and somewhat truncated in the Cyclonema. 



Formation and locality. Shales of the Black River group (Ctenodonta bed chiefly), Minneapolis, St. 

 Paul, Cannon Falls, Chatfleld and Fountain, Minnesota. Also, though very rarely, in the Clitambonites 

 Oed of the Trenton group, at St. Paul. In Kentucky it occurs near Burgin in the upper part of the 

 Trenton. 



Collections. Geological and Natural History Survey of Minnesota; E. O. Ulrich; W. H. Scofleld. 

 Museum Register, No. 233. 



Genus HOLOPEA, Hall. 

 Holopea, HALL, 1847, Pal. N. Y., vol. i, p. 169. 



Though we have given considerable study to the matter, we prefer not to 

 commit ourselves at present to a description of the generic characters. We may 

 say, however, that Holopea, as now used, embraces much that does not belong here. 

 Indeed, some of the following species doubtless will be removed when the contents 

 of the genus re finally revised. Most diverse affinities are indicated by different 

 sets of species, some evidently being true LiUorinida>, others are related to Cyclonema 

 and Strophostylus, another set to Platystoma, while a few are difficult to place. 



