122 New Upper Silurian Fossils. 



Genus TBEMATIS, Sharp. 



TREMATIS (SCHIZOCRANIA) SUPERINCRETA, New Species. 



The upper valve of a patelliforin shell, externally like the 

 Orbicula (?) filosa, H.,= Trematis filosa, H., = Schizocrania 

 filosa, H. and W., is found, very rarely, in the Trilobite layers, 

 or uppermost Lower Helderberg strata, of this village. It is 

 twice or thrice as large as that shell, broadly ovate in general 

 outline, convex, highest behind the middle, and widest an- 

 teriorly. Apex obtuse, marginal. Surface jet black, shining, 

 radially marked by elevated filiform striae, which are more or 

 less arcuate toward the beak. Very fine concentric striae 

 cross these, preserving their full size over them, and impart- 

 ing to them a sub-nodose or slightly moniliform appearance. 

 Stronger concentric lines and laminations of growth are inter- 

 mixed with these very fine concentric ones. Eadiating striae 

 arising independently, rarely if at all bifurcating, ten to 

 twelve in the width of one line over the rostral region, five to 

 eight in the same space nearer the front. Length and width 

 of valve sub-equal, from twelve to fifteen lines in the largest 

 specimens yet seen. Lower valve, and internal markings of 

 upper valve, unknown. 



One or two valves have been seen attached to larger shells, 

 precisely like specimens of Schizomania filosa, from the Cincin- 

 nati Group. One was fixed upon a large Strophomena, its 

 margin conforming to all the external inequalities of the 

 larger shell, and spreading widely over its surface. It must 

 have grown in that position, and have been, like the Schizo- 

 crania (?) filosa, parasitic. Other valves have been found in a 

 similar position, but not with the spreading margin. In the 

 absence of the lower valve, I can see no reason for not 

 referring this shell to the same genus with the Trematis 

 ( Schizocrania ) filosa H., and H. and W. It has been labeled 

 Trematis by Prof. Hall, perhaps without being aware of its 

 parasitic habit. But it seems to me to be very questionable, 

 notwithstanding the eminent authorities upon the other side, 

 whether parasitic habits alone can justify the erection of the 

 new genus Schizocrania. I prefer, until its generic position is 

 better established, to place it, provisionally at least, under 



