952 THE PALEONTOLOGY OF MINNESOTA. 
[Synopsis of Pleurotomariide. 
II. Scnizotopwa, n. gen. (Ulrich.) In every respect like Lophospira excepting 
that the apertura] notch is prolonged into a long parallel-edged slit. Type, S. 
textilis, n. sp. (Ulrich.) 
II]. PHanrerotrema, Fischer, 1885.* Shell turbinate, whorls few in number, 
flattened above, the last large and high, the others rising step-like; spire short; slit 
long, region of band salient; aperture subquadrate, inner lip thick; lines of growth 
nearly vertical beneath the band, above it turning more decidedly forward; strong 
revolving lines occur especially on the lower and outer parts of the whorls. Type, 
P. labrosa Hall. 
This Upper Silurian genus seems to have been derived from the Tvrochonemoides 
section of Lophospira, our L. trochonemoides and L. knoxvillensis being very similar in 
general form and having almost exactly the same kind of aperture. The band, 
though salient also in those species, is somewhat different, the central line being, as 
it should be in Lophospira, considerably stronger and more prominent than the 
bordering lines. Still, in our opinion, the peculiarities of the Jabrosa type of band 
were produced by an extreme development of the bordering lines, the space between 
the elevated edges being gently convex. Aside from the band, Phanerotrema is 
distinguished from all the Lower Silurian Pleurotomariide, except Schizolopha, by its 
long slit, and from the excepted genus by its relatively smaller spire, much larger 
last volution, peculiar band, and strong revolving lines. Further, it seems very 
clear that, although both types originated in Lophospira and deviated from the 
general character of that type in similar directions, their immediate ancestors 
represent widely different sections of that genus, and constitute distinct lines of 
development. Of the two species of Schizolopha, S. textilis evidently came from the 
Bicincta section, while S. mooresi accords more nearly with the Perangulata section. 
As to Phanerotrema, we have already said that it was most probably derived from 
the T'rochonemoides section. 
Phanerotrema includes besides the type species, PJ. occidens Hall, and a Goth- 
landic shell which Lindstrém erroneously identified with Hall’s labrosa. The genus 
appears to be sparingly represented in the Devonian of Europe, but we know of 
none in American deposits of that age. Two of our Carboniferous species, however, 
Pl. grayvillensis Norwood and Pratten, and Pl. marcouiana Geinitz, appear to have all 
the essential characters of Phanerotrema, and we expect to find that they are actual 
continuations of the same generic type. 
1V. Worrtuentra, De Koninck, 1883. Shell conical, tabulate, the general aspect 
much as in Lophospira; whorls angular on the periphery, the latter carrying the 
band; slit extending backward from the mouth between one-fourth and one-third of 
* Manual de Conchyliologie, p. 851. 
