FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 109 



Spirifera byrnesi. *. SP. 



Plate X., figures 1-5, 31-34 and 36-39. 



Shell sub quadrate, semi-circular and gibbous in outline; hinge-line equalling 

 greatest width of shell and terminating in salient angles. Surface plicate. 



Ventral valve ventricose and only little more gibbous than other valve; regu- 

 larly arcuate from beak to front ; greatest convexity in the upper part a little 

 above the middle, from where it curves regularly to the front and sides ; beak 

 much elevated above hinge-line, and slightly arcuate. Cardinal area high, 

 concave, and extending to cardinal angles, where it never forms an acute angle, 

 but shows always a height of from one-quarter to one- half of a line, a feature 

 which is not sufficiently expressed in the figures on plate 10 ; mesial sinus 

 sharply defined, forming a deep triangular groove, with an acute angle at the 

 bottom, much produced in front ; fissure of medium size. 



Dorsal valve gibbous, with a greatly elevated mesial fold, which is edged in 

 its upper part and rounded below ; beak little elevated and slightly inclined 

 over a narrow hinge-area. Surface marked by from eight to ten very prominent 

 and angular plications on each side of the mesial fold and sinus, which are 

 crossed by strong imbricating concentric lines of growth, showing more promi- 

 nently in front than in upper portion of shell. Of the plications, the lateral 

 ones do not reach to the beak, but run out on the margins of the cardinal 

 area. 



The dimensions of this species are as follows : it measures from one-half to 

 three-fourths of an inch in length, and from three-fourths to seven-eighths of 

 an inch in width ; its width always exceeds its length. 



This species takes an intermediate position between Spir. gregaria and Spir. 

 varicosa ; it is more transverse than the former, and less so than the latter ; its 

 umbo is less elevated and curved than that of gregaria, and more so than that 

 of varicosa ; its deeper and sharply angular sinus, and its more elevated fold, 

 distinguish it from both of its relations. It is a well marked and easily 

 recognized species. 



Formation and Locality. Found in the upper strata of the Devonian limestone around the Falls 

 of the Ohio, in Kentucky and Indiana. Very fine specimens I found in considerable numbers in the 

 quarries at Lexington, Indiana. I dedicate this species to Dr. K. M. Byrnes, of Cincinnati, Ohio, who 

 devotes all his spare time to the study of geology and palaeontology, and who greatly contributed to our 

 knowledge of the Cincinnati fossil fauna. 



