No. 109.] 169 



finer, and under a magnifier they present the granulated surface which 

 sufficiently distinguishes them from all other species in our strata. 



Geological position and locality. Shales of the Hamilton group : Mos- 

 cow, Livingston county ; and Daricn, Genesee county. 



SPIRIFER^ OF THE CHEMUNG GROUP. 



Spirifer textus (n.s.). 



Pal. N.Y. Vol. iv. 



Shell large, somewhat thin, semicircular or sub-semicircular, 

 one-third to one-half as long as broad ; height often greater 

 than the length ; hinge equalling the greatest width of the shell, 

 and terminating in more or less salient angles at the extremities : 

 dorsal valve convex, most prominent near the front, rising in 

 the middle into a rounded mesial fold, which diminishes regu- 

 larly and somewhat rapidly from the front ; beak, together with 

 the narrow area, distinctly arched : ventral valve much more 

 convex, very prominent at the umbo, from which it slopes at 

 an angle of about 100° towards the lateral margins, and more 

 abruptly to the front; mesial sinus deep, rapidly increasing 

 from beak to front, where it occupies about one-fourth of the 

 anterior margin, terminating in a broad projection with a rounded 

 extremity ; beak angular, far removed from the hinge by the 

 high intervening area, nearly straight or slightly arched towards 

 the extremity ; area very large and high, plane below ; foramen 

 large triangular, about two-thirds as broad as high. Surface 

 marked by about twenty simple depressed and rounded plica- 

 tions on each side of the mesial fold and sinus : plications 

 crossed by fine irregular undulating concentric lines of groT^th. 

 Entire surface delicately and beautifully marked by minute 

 elongated pits, so disposed as to present under a magnifier the 

 appearance of twilled cloth. 

 This fossil has been regarded asidectical with S. cuspidatus of Martin ; 



but the much greater number of plications, as well as the peculiar surface 



