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 Lindstrém 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, 2. Sp. 
PLATE LXXXII, FIGS. 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 ina ventral view, but whena 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 striw is stronger than the other. Cyclonema gracile 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 aad somewhat truncated in the Cyclonema. 
Formation and locality.—Shales of the Black River group (Ctenodonta bed chiefly), Minneapulis, St. 
Paul, Cannon Falls, Chatfield and Fountain, Minnesota. Also, though very rarely, in the Clitambonites 
ded 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 vf Minnesota; E. O. Ulrich; W. H. Scofield. 
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 are finally revised. Most diverse affinities are indicated by different 
sets of species, some evidently being true Littorinida, others are related to Cyclonema 
and Strophostylus, another set to Platystoma, while a few are difficult to place. 
