GASTROPODA. 991 



eblaolopk*.) 



peripheral space they are apj* <>n Die base broadly recurved about as ID L. k*atriUe**u 



and L. trocbtmimoidu. 



The most striking featurv n( thl* remarkable hell, and one that will distinguish It at once from 

 every <>nc ? the hint ..f !.. r Silurian I'lettmtomarUda. known to us, IN the coarsely marked Hilt-band. 

 Tin-. as well as tin- f..nu <>f tho aperture and, In fact, the general aspect of the whole shell, Is so dllT 

 rr. .in MI- uMial type* of Lopliotpira that. If we had not at the tame time seen L. knoxriUfnti* and //. irocho- 

 nemoidet which, while having the usual I^phatfrim band, yet agree very closely with It In all other respects, 

 we would hav. red ourselves justlfled In proposing a new genus for Its especial beneflt. As It Is, 



we arc not at all satisfied that It would not be better to set these three species apart as a distinct genus, 

 > facilitating reference to a genetic relationship that before the discovery of these shells was not 

 ^uspected. That a relation ! this kind does exist between Trochonema and the I'leurotnmaHidie Is 

 now scarcely to be denied, for It seems almost Inconceivable that such Intimate agreement In strurtun- 

 ept In near branches of the same stock. For further remarks on this group of species see 

 under L. Icnranllentii. 



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 Plenrofomariiilir, the two species of this genus 

 alone po MOM 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 



/.oan, 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. moorei the slit extends backward for a distance 

 equaling about one-fifth of the circumference of the last whorl, in S. lexlilis 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. 



Schvzolopha 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 cjuite as much. The last species is represented in the 

 collections before us, and we can say most positively that it is not a Lophospira. 

 I Living a concave band, situated somewhat obliquely upon the periphery, it had 

 perhaps best be placed under Eotomarin, though scarcely as a good species of that 

 genus. Having a concave band and agreeing also in all other respects, save in wanting 

 a slit and revolving surface markings, we believe we have in I/ophospira or Kotomaria 

 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. 



