GASTROPODA. 991 
Schizolopha.] 
peripheral space they are approximately vertical, on the base broadly recurved about as in L. knoxvillensis 
and ZL. trochonemoides. 
The most striking feature of this remarkable shell, and one that will distinguish it at once from 
every one of the host of Lower Silurian Pleurotomariide known to us, is the coarsely marked slit-band. 
his, as well as the form of the aperture and, in fact, the general aspect of the whole shell, is so different 
from the usual types of Lophospira that, if we had not at the same time seen L, knoxvillensis and L. trocho- 
nemoides which, while having the usual Lophospira band, yet agree very closely with it in all other respects, 
we would have considered ourselves justified in proposing a new genus for its especial benefit. As it is, 
we are not at all satisfied that it would not be better to set these three species apart as a distinct genus, 
thereby facilitating reference to a genetic relationship that before the discovery of these shells was not 
even suspected. That a relation of this kind does exist between Trochonema and the Pleurotomariide is 
now scarcely to be denied, for it seems almost inconceivable that such intimate agreement in structure 
could occur except in near branches of the same stock. For further remarks on this group of species see 
under L. knoxvillensis. 
Formation and locality.—Black River group (Carter’s Creek limestone) Maury county, Tennessee, and 
Mercer county, Kentucky. 
Genus SCHIZOLOPHA, Ulrich. 
For generic characters see page 952. 
Of all the known Lower Silurian Pleurotomariide, the two species of this genus - 
alone possess a true apertural slit. In both the length and actual presence of the slit 
were established by the fact that a parasitic crust, in one case of a coral, in the other a 
bryozoan, which covered the shells evidently during life, grew up to but not over 
the slit and thus left a narrow space uncovered corresponding in width and length 
with the slit in the shell. In S. mooret the slit extends backward for a distance 
equaling about one-fifth of the circumference of the last whorl, in S. textilis about 
two-ninths. The general expression of the two shells reminds one strongly of 
Lophospira, and when we add that the slit-band is of the convex type, we believe we are 
fairly justified in assuming that they were derived from some member of that genus. 
Schizolopha may be compared with Phanerotrema, Fischer, an Upper Silurian and 
Devonian genus, also provided with a long slit but differing in having a concave 
slit-band. Phanerotrema reminds one in some respects very strongly of the Trocho- 
nemoides section of Lophospira, but it recalls in other features the Calciferous 
Lophospira cassina Whitfield quite as much. The last species is represented in the 
collections before us, and we can say most positively that it is not a Lophospira. 
Having a concave band, situated somewhat obliquely upon the periphery, it had 
perhaps best be placed under Hotomaria, though scarcely as a good species of that 
genus. Having a concave band and agreeing also inall other respects, save in wanting 
a slit and revolving surface markings, we believe we have in Lophospira or Eotomaria 
cassina a reasonably plausible progenitor for Phanerotrema—certainly a more likely 
one than any of the forms that we refer to Lophospira. If this is correct, then 
Schizolopha and Phanerotrema must be maintained as representing two distinct 
though almost parallel lines of development. 
