FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 60 



are noticed on each half of the cardinal margin, but this is subject to varia- 

 tion, as the number may differ from two to four. Figure 19, plate 17, is 

 enlarged, and figures 19 and 20, on plate 31, show an elongate form. 



Formation and Locality. Occurs in the hydraulic limestone, in Jefferson county, Ky., and in 

 Clark county, Indiana, and is somewhat abundant in well preserved specimens. Prof. Hall named this 

 species in honor of the late Dr Lunsford Yandell, Sr., of Louisville, Ky., who was one of the first col- 

 lectors of fossils from the Falls of the Ohio. 



Genus Productella. Han. 



Productella, Hall. Pal. N. Y., Vol. IV., page 1531867. 

 Etymology . Productella, diminutive of Productus. 



Shell having the general form of Productus, but uniformly, with a narrow 

 area on each valve, a foramen or callosity on the ventral area, small teeth, and 

 more or less distinct teeth-sockets. The reniform vascular impression, rising 

 from between the anterior and posterior muscular impressions, curves gently 

 outwards, and following a curvature [somewhat parallel with the margin of the 

 shell to below the middle of its length, is abruptly recurved and the extremity 

 turned a little backwards, terminates about half way between margin and 

 anterior extremity of mesial septum. The cardinal process, seen from the 

 inner side, is bilobed, and from the exterior side each of these divisions is 

 usually bilobed. These shells differ from Stropholosia in the extremely narrow, 

 linear cardinal area, greater extension of hinge-line, more extreme arcuation 

 or ventricosity of ventral valve in many or most of the species, and especially 

 in the direction and termination of the reniform vascular impressions, which 

 resemble those of Aulosteges, and of some of Productus. It differs from Pro- 

 ductus by the constant presence of an area, hinge-teeth and sockets. 



Productella subaculeata var. cataracta. HALL AND^WHITJ-IELD 



Plate XVII., figures 6 to 9. 



Productella subaculeata var. cataracta, H. and W. 24th Regent's Keport, p. 198 1872. 

 Productella subaculeata var. cataracta, H. and W. 27th Regent's Rep., pi. 9 1875. 



Shell small, semi-globose, rounded; hinge-line straight and about equal to 

 width of shell; length and width of shell about equal. Ventral valve very 

 gibbous, regularly curved from umbo downward, and also transversely ; umbo 

 is considerably elevated above hinge-line, and the beak is small and incurved. 

 The lateral margins form with the cardinal line nearly right- angles; they are 

 a little contracted below the extremities, forming small ears ; below the ears 

 the sides are regularly curved, and the front is broadly rounded. The dorsal 

 valve is deep concave, as shown in the specimen illustrated on plate 17, figures 

 5 and 6. Said specimen is nearly perfect in both valves, and entirely free from 



