PLATE LXVIII. 



(FiKaro8 l-« by E. EMHOM8.) 



Gends PENTAMERUS, Sowerby. 



Page 236. 



Pentamerus OBLONGU8, Sowerbv. 



FigB. 1, 2. Dorsal \-iew8 of two shells ; showinjr the variation in outline assumed by the species at this local- 

 ity. Figf. 1 (see also plate Ixix, fig'. 7) approaches the subquadrate outline of P. ohlongus, var. 

 gubrectus (see tip- 6 and plate Ixix, figfs. 8-10), but has less conspicuous urabones 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. 



Fly. 8. Dorsal \-iew of a large, elongate shell, with a broad median lobe. 



Fly. 4. Ventral view of another specimen of similar character, the two lateral grooves defining the median 

 and U.teral lobes being very strong. The specimen shows the cavity of a very short median 

 septum. 



Pig. 6. 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 

 mach too conspicuous in the figure. 



Niagara dolomites. Yellow Springs, Ohio. 



Pentamerus oblongus, var. subrectus. var. uov. 



See Plate Ixix. 

 Pig. 6. Dorsal view of a large individual of this variety slightly impeifect at the anterior margin ; show- 

 ing the subquadrate outline, medially convex and bro.idly lobed valves. 

 Niagara beds. JoTies county, Iowa. 



Pentamerus oblongus, var. cylindricus, Hall and Whitfield. 



Pigs. 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. 



