410 TRANS. OP THE ACAD. OP SCIENCE. 



rounded, and the lateral plication on the fold and in the sinus 

 are larger than in the true Leidyi. 



This fossil is very similar to the Spirifer Keokuk, var. of 

 Prof. Hall (Iowa Report, PI. xxiv., fig. 4, a, b, d) ; but it oc- 

 curs in the Ste. Genevieve Limestone, associated with the S. 

 Leidyi, above the St. Louis Limestone. 



Variety, Merimacensis. 



This variety has the general appearance of the Leidyi ; 

 but its plications are much larger, about seven on each side 

 of the mesial fold and sinus ; mesial fold high, with two pli- 

 cations — no smaller ones on the sides as in the Leidyi. 



It is a rare fossil in the Archimedes Limestone at Barrett's 

 Station on the Pacific Railroad, Missouri. 



Spirifer increbescens, Hall. 

 Variety, Americana. 

 This shell is much smaller than the true increbescens ; has 

 fewer costas ; the mesial fold and sinus are much more sharp- 

 ly defined; the sinus is more depressed and the fold more 

 elevated. It is more semi-elliptical, and is not so full on each 

 side between the mesial sinus and the lateral margins. 



The Americana is easily distinguished by its size, form, 

 number of plications, and its more sharply defined mesial fold 

 and sinus. This shell is found at the base of the Kaskaskia 

 Limestone, in Missouri and Illinois. 



Spirifer Keokuk, Hall. 

 Variety, Shelbyensis. 

 Shell larger, plications higher and more numerous — about 

 fourteen on each side of the sinus. 



This fossil occurs in the Archimedes Limestone in Shelby 

 county, Missouri. 



Descriptions of New Species of Bryozoa. By Dr. Hiram 

 A. Prout. 



[The following descriptions of new species of Bryozoa were placed in 

 my hands for publication by M. L. Gray, Esq., administrator of the estate 

 of the late Dr. Prout. — B. F. Shumard.J 



8-10 l. 

 10-12 t. 



Fenestella nodosa, Prout. 



Bryozoum, a fan-shaped expansion, with small, round, 

 longitudinal rays, regularly distributed, and without the ap- 

 pearance of dissepiments or nodes to the naked eye. 



Longitudinal rays uniform, straight, round, bifurcating 

 from one to one and a half lines apart, presenting under the 

 microscope regular lines of nodes or tubercles, slighty longer 

 than broad, about their own length apart and having no cor- 



