PLATE LXIX. 



(Fimirea 1-10, IS by G. B. SiMrgON; 11, 1» by K. P. Whitfield. ) 



Genus PENTAMERUS, Sowerby. 



Page 236. 



Pentamerus OBLONGU8, Sowerby. 



fig. 1. Doroal view of an internal cast of a small shell, broadly trilobed and having a similar outline to 

 youn^ forms of the variety subrectus (see tig-s. 2, 3) though with much shallower valves. 

 Niagara dolomites. Richmond, Indiana. 



Pentamerus oblongus, var. subrectus, van iiov. 



tiee Plate t>8. 



Figs. 2, 3. Dorsal and ventral views of a small specimen of subquadrate outline, trilobed exterior, and 



showing the single median septum in both valves. 

 Figs. 8-10. Dorsal, pn>file and ventral view.s of a noi-mal matui"e individual ; showing the characteristic 



subquadrate outline, prominent umbo of the pedicle-valve, trilobate exterior, and linear median 



depression on both valves. 



Niagara beds. Castle Orove tovmship, Jones county, Iowa. 



Pe.\tamerus oblongus, Sowerb}'. 



Figs. 4, 6. Dorsal and venti-al views of a small elongate internal cast in chert, similar in contour and size 

 to a form occurring at Utica, Indiana, in association with the variety cylindrlcus. This shell 

 occurs in the chert of the Maquoketa region near Dubuque, Iowa, but not in immediate asso- 

 ciation with the var. subrectus. 



Niagara beds. Jones county, Iowa. 

 Fig. 6. Dorsal view of the umbonal region of an interaal cast in chei-t ; showing the cavities left by the 

 septum and septal plates, the deltidium and the lateral divisions of the hinge-plate. X 2. 

 Niagai-a beds. Monmouth, Iowa. 

 Fig. 7. Ventral \-iew of a subquadrate shell with the lobation of the surface distinctly defined. The dor- 

 sal view of this specimen is given upon plate Ixviii, fig. 1. 

 Clinton group. Rochester, New York. 



Pentamerus oblongus, van cylindricus, Hall and Whitfield. 



FlgB. 11, 12. Profile and dorsal views of the original specimen of this variety ; showing the elongate form 

 and a faint trilobation of the exterior. 



Niagara group. Near Louisville, Kentucky. 



Pentamerus oblongus, Sowerby. 



Pig. 13. Dorsal view of an internal cast of a large and evenly convex shell having the ovoid form and 

 regular contour of the var. Maquoketa (see plate Ixvii, figs. 11-13), which, however, is a per- 

 sistently smaller form. 



Niagara dolomites. Locality uncertain ; probably Northern Indiana. 

 Pig. 14. An outline sketch of a large brachial valve having the broadly ovate form and trilobed exterior 

 of the specimens from Yellow Springs, Ohio, represented on plate Ixviii, figs. 3-6. 

 Niagara dolomites. Proltahly from the vicinity of Richmond, Indiana. 



