FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 119 



east of the city of Louisville, where it is rare, generally, but more so in well preserved individuals; only 

 a few specimens of this species are to be found in the different cabinets of the Falls Cities. It affords me 

 great pleasure to name this species in honor of my friend, the noble-hearted and venerable Mr. Fogg, of 

 Jeffersonville, Indiana. 



Spirifera gregaria. CLAPP. 



Plate VIII., figures 9 to 13, and Plate X., figures 6 to 10. 



Spirifer gregaria, Clapp. MS. 



Spirifer gregaria, Hall. Tenth Kep. on the State Cab., p. 127 1857. 

 Spirifer gregaria, Clapp. Billings in Canadian Jour., p. 128 1857. 

 Spirifera gregaria. Hall. Pal. N. Y., Vol. 4, p. 195, plate 28. 



Shell ventricose, sub-globose, semi-oval or sub-quadrate in outline ; hinge- 

 line usually equal, but sometimes less than width of shell ; cardinal extremities 

 truncate or somewhat rounded. Surface plicated. 



Ventral valve very gibbous, and more so than the dorsal valve ; it is regularly 

 arcuate from beak to front. Its greatest convexity is at or a little above the 

 middle, from where it curves somewhat abruptly to the sides, but more gently 

 to the front ; beak much elevated, and apex closely incurved over the 

 fissure; area high, concave and extending to the cardinal angles, where it is 

 sometimes more than half a line high, often distinctly striated ; mesial sinus 

 rounded or sub-angular and much produced in front. 



Dorsal valve very convex with a strong mesial fold, either angular or some- 

 what flattened along the summit, and sometimes marked by an indistinct 

 groove ; beak often considerably elevated, and slightly inclined over the 

 hinge area, which is narrow except in the center, where it widens perceptibly 

 Surface marked by from six to ten strong rounded ribs on each side of the 

 mesial fold and sinus. The entire surface is covered with undulating con- 

 centric striae, which, towards the front, become strong zigzag imbricating 

 lines of growth, resembling somewhat the front ornamentation of Spirifera 

 davisi. 



The interior of the ventral valve presents a well defined, oval, muscular 

 impression, with a low crest in the center. The dental plates are often much 

 thickened, filling the entire rostral cavity, and encroaching upon the muscular 

 area. 



The width of this species ranges from one-half to seven-eighths of an inch, 

 and the length is usually a little less than the width; but there are some speci- 

 mens in which the length equals or even exceeds a little the width, as may 

 be seen in the one figured on plate 8. In very gibbous specimens the beak 

 of the ventral valve is so extremely elevated, that almost one-half of the ven- 

 tral valve is above the cardinal line. In the majority of specimens there are 

 six or seven plications on each side of the mesial fold or sinus. The variable 



