PLATE LXVIII. 



(FigurCb 1-8 by E. EMMON8.) 



Genus PENTAMERUS, Sowerby. 



Page 236. 



Pentamerus oblongus, Sowerby. 



FigB. 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) apjiroaches the subquadrate outline of P. ohlongus, var. 

 suhrectus (see fig. 6 and plate Ixix, figs. 8-10), but has less conspicuous umbones and less con- 

 vex valves ; fig. 2 has a peculiarly triangular outline, which is I'eproduced with a strongly 

 trilobate anterior margin in the larger specimens from Yellow Springs, Ohio (see figs. 3-5). 

 Clinton group. MocJiester, New York. 



Fig. 3. Dorsal view of a large, elongate shell, with a broad median lobe. 



Fig. 4 Ventral view of another sjiecimen of similar character, the two lateral grooves defining the median 

 and lateral lobes Leing very strong. The .specimen shows the ca\-ity of a very short median 

 .septum. 



Fig. 5. Dorsal view of a smallei' 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 \ery faint and have been made 

 much too conspicuous in the figure. 



Niagara dolomites. Yellow Siyri?i,gs, Ohio. 



Pentamerus oblongus, var. suhrectus. var. iiov. 



See Plate Ixix. 

 Fig. 6. Dorsal view of a large individual of this vanety slightly imperfect 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 Wliitlielcl. 



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. Utiva, Indiana. 



