PLATE LXVIII. 
(Figures 1-8 by E. Emmons.) 
Genus PENTAMERUS, Sowerby. 
Page 230. 
Pentamerus oblongus, Sowerby. 
Fig'S. 1, 2. Dorsal views of two shells ; showing the variation in outline assumed by the species at this local¬ 
ity. Fig. 1 (see also plate Ixix, fig. 7) ajiproaches the subquadrate outline of P. oblongus, var. 
subrectus (see fig. 6 and plate Ixix, figs. 8-10), but has less consjiicuous uinbones and less con¬ 
vex valves; fig. 2 has a peculiarly triangular outline, which is reproduced with a strongly 
trilobate anterior margin in the larger specimens from Yellow Springs, Ohio (see figs. 3-5). 
Clinton group. Rochester, New York. 
Fig. 3. Dorsal view of a large, elongate shell, with a broad median lobe. 
Fig. 4. Ventral view of another specimen of similar character, the two lateral grooves defining the median 
and lateral lobes being very strong. The specimen shows the cavity of a very short median 
septum. 
Fig. 5. Dorsal view of a smaller specimen, less distinctly trilobed, but with the umbo of the pedicle-valve 
very broad, though slightly imperfect at the apex. (Compare in this respect plate Ixix, fig. 8.) 
The lateral undulations on the brachial valve are actually very faint and have been made 
much too conspicuous in the figure. 
Niagara dolomites. Yellow Spo-ings, Ohio. 
Pentamerus oblongus, var. subrectus, var. iiov. 
See Plate Ixix. 
Fig. 6. Dorsal -view of a large indi%ddual of this variety slightly impei'fect at the anterior margin j show¬ 
ing the subquadrate outline, medially convex and broadly lobed valves. 
Niagara beds. Jones county, Iowa. 
Pentamerus oblongus, var. cylindricus. Hall and Whitfield. 
Figs. 7, 8. Dorsal and ventral views of a characteristic example of this variety; showing the extremely 
elongate-elliptical outline and broadly trilobed exterior. 
Niagara dolomites. Utica, Indiana. 
