FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 115 



Spirifera dubia. N.BP. 



Plate XXXIII., figures 23 and 24. 



This shell I found in the strippings of a quarry east of the city of Louis- 

 ville, where the top rocks belong to the Devonian, and the lower strata to the 

 Silurian ; it is. therefore, impossible to state to which of these formations it 

 belongs. It further has in form and outline great similarity with Spir. crispa, 

 var. simplex, from which it, however, differs greatly in other points. Concern- 

 ing this shell there is, therefore, doubt in regard to its formation, and also 

 whether or not it should form a new species, and for these reasons I think it 

 fully deserves its specific name. 



Shell small, semi-circular or semi elliptical and ventricose. Convexity of 

 both valves almost equal ; hinge line less than greatest width of shell ; cardinal 

 extremities rounded. Surface without plications. 



Ventral valve ventricose, having its greatest convexity a little above the 

 middle of the shell, from where it curves regularly and markedly to the 

 anterior and lateral margins. Mesial sinus extends from beak to front, shallow 

 in the upper part, deepening and widening towards the base ; angular in the 

 bottom, but its margins not at all defined ; in front it forms a pretty strong 

 triangular extension. Cardinal area elevated, with undefined rounded mar- 

 gins ; beak arcuate, but. not incurved over a high and narrow fissure. 



Dorsal valve almost as convex as the other, having its greatest convexity a 

 little above the middle, from where it curves regularly towards the front and 

 sides. Mesial fold not at all noticeable on the umbo ; little elevated and sub- 

 angular towards the base ; beak incurved over a narrow area. 



Surface having not the least trace of plications, but covered by lamellose, 

 imbricating, concentric striae, similar to those in Spir. var. simplex. Size of 

 shell is three-eighths of an inch in length, and a little less than one-half of an 

 inch in width. 



Formation and Locality. The formation from which it comes uncertain as above stated ; found in 

 a quarry east of the city of Louisville. This one specimen the only one so far known, 



Spirifera euruteines. OWEN. 



Plate VI., figures 1 to 7; 9, 11 to 17. 



Delthyris (Spirifer) euruteines, Owen. Report of Geological Exploration in Iowa, Wisconsin and Illinois. 

 Spirifer euruteines, Owen. Geol. Surv. of Wise., Iowa and Minn., p. 586, Tab. III., figs. 2 and 2a, and 



6, 6a, b. 

 Spirifera euruteines, Hall. Pal. of N. Y., Vol. IV., page 209, plate 31, figures 14 to 19. 



This species was first described and figured by Prof. David Dale Owen, in 

 his report on the Geological Survey of Wisconsin, Iowa and Minnesota, from 

 specimens found on Pine creek, Iowa. Owen states that this is the same shell 



