PLATE LXIX. 



(Kiguies 1-10, 13 liy G. B. SIMPSON; 11, 12 by K. P. Whitfield ) 



Genus PENTAMERUS, Sowerby. 



Pago 236. 



Pentamerus oblongus, Sowerby. 



Fi^. 1. Dorsal view of an internal cast of a small shell, broadly trilobed and having- a similar outline to 

 young forms of the \-ariety suhrectus (see tigs. 2, 8) though with much shallower valves. 

 Niagara dolomites. Richmond, Indiana. 



Pentamerus oblongus, vur. subrectus, vnr. nov. 



See Plate 68. 

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



showing the single median septum in both valves. 

 Figs. 8-10. Dorsal, jirofile and ventral views of a normal 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 Gfrove township, Jones eounty, loioa. 



Pentamerus oblongus, .Sowerby. 



Figs. 4, 5. Dorsal and ventral 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 ryiindrii-us. This shell 

 occurs in the chert of the Ma(iuoketa region near Dubuc^ue, Iowa, liut not in immediate asso- 

 ciation with the var. suhrectus. 



Niagara beds. Jones county, Iowa. 

 Fig. B. Dorsal view of the umbonal region of an internal cast in chert ; showing the cavities left by the 

 septum and septal plates, the deltidium and the latei'al divisions of the hinge-plate. X 2. 

 Niagai-a beds. Monmouth, loipa- 

 Fig. 7. Ventral view 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, vur. cyllvdricus. Hall iiiul Whitliekl. 



Figs. 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, Sowerliy. 



Fig. 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. 

 Fig. 14. An outline sketch of a large brachial ^•alve having the broadly ovate form and trilobed exterior 

 of the specimens from Yellow Springs, Ohio, represented on plate Ixviii, figs. 3-5. 

 Niagara dolomites. Probably from the vicinity of Richinond, Indiana. 



