318 PROCEEDINGS OF THE ACADEMY OP 



This very delicate little form will be readily distinguished from 

 the other known Silurian species b}' its small size and peculiar 

 plumose mode of growth, and particularl}' by its very minute 

 strijB between the pores. Sfictopora raripora^ Hall, from the 

 Clinton group of New York, is as delicate a form, but differs ma- 

 terially in its mode of growth, and particularly in its very much 

 less numerous pores. 



The specific name is given in honor of Mr. D. H. Shaffer, of 

 Cincinnati, Ohio, to whom I am indebted for the use of a very 

 fine specimen of it ; I also have good specimens from Mr. Dyer's 

 collection. 



Locality and ]position. — Toward the lower part of the Cincin- 

 nati group of the Lower Silurian at Cincinnati, Ohio. 



BRACHIOPODA. 



RETZIA (TREMATOSPIRA) GRANTJLIFERA, Meek. 

 Shell transversely oval, the length being about four-fifths the 

 breadth, moderately convex, the convexity of the two valves 

 being very nearly equal ; lateral margins rather narrowly rounded 

 in outline ; front and anterior lateral margins broadly rounded, 

 or perhaps the former sometimes straight or slightly sinuous in 

 outline in the middle ; cardinal margin nearly straight on each 

 side, and sloping at an angle of about 140'^ from the beaks to- 

 ward the lateral extremities. Dorsal valve nearly evenly convex, 

 its greatest prominence being perhaps slightly behind the mid- 

 dle ; provided with about tliirteen simple, angular, radiating plica- 

 tions or costse, five of which on the middle are smaller than the 

 others (the middle one being smallest and not continued to the 

 beak), and form together a very low, flattened mesial elevation, 

 scarcely rising above the general convexity ; beak rather strongly 

 incurved. Ventral valve of much the same form as the other, 

 excepting that its beak is somewhat more prominent, perforated,^ 

 and incurved upon that of the other valve ; while two of the 

 middle costse are much smaller than the others, and the first one 

 on each side of these is intermediate in size between the smallest 

 central ones and the largest on the lateral slopes ; these four 



' The immediate point of the beak of the ventral valve seems to be slightly 

 broken in the specimen, though it has the appearance of having been natu- 

 rally perforated before receiving the slightest injury. 



[February 13, 



