Repobt of the State Geologist. 



gin, and is sharply delimited by abrupt lateral slopes. The sides 

 of the valve are convex, rather narrow, and slope abruptly to the 

 lateral margins. Umbo full and incurved. Surface covered with 

 numerous duplicating plications, of which from fifteen to twenty 

 may be counted on each side at the margins, and twelve to four- 

 teen in the fold. 



Clinton group. Trenton^ Georgia. 



Pentamerus obl9ngus, Soweeby, var. Maquoketa. 



Plate 11, figs. 12-14. 

 Pentamerus oblongus, var. Maquoketa, Hall. Palaeontology of N. Y., vol. 

 YIII, pt. 3, expl. pi. Ixvii, figs. 11-13. 1894. 



Shells small, with highly ventricose valves ; general aspect 

 ovoid. Umbo of the pedicle valve not greatly elevated. Mar- 

 ginal outline suboval. Surface smooth. Spondylium well 

 developed in the pedicle-valve ; septal plates of the brachial valve 

 not uniting. 



Niagara dolomites. J^^ear Dubuque, Iowa. 



Pentamerus oblongus, Soweeby, var. subrectus. 



Plate 12, figs. 1-6. 



Pentamerus oblongus, var. subrectus, Hall. Palaeontology of N. Y. , vol. VIII, 

 pt. 2, expl. pi. Ixviii, fig. 6; pi. Ixix, figs. 2, 3, 8-10. 1894. 



Shells with elongate, subquadrate marginal outline, high, sub- 

 rectangular cardinal extremities, narrow and exsert umbo. 

 Yalves subequally convex, the greatest convexity being from 

 umbo to anterior margin along the median axis. Each valve 

 bears a longitudinal impressed median line and two divergent 

 grooves which divide the surface, into three divisions or fault 

 lobes. Surface smooth ; sometimes with traces of obscure, coarse 

 radial folds in the median region. 



Niagara group. Jones county, Iowa. 



Capellinia mira. 



Plate 13, figs. 5-13. 

 Capellinia mira, Hall. Palaeontology of N. Y., vol. VIII, pt. 3, p. 249, pi. Ixx, 

 figs. 6-14. 1894. 

 Shells large, elongate subovate. The relative size and convex- 

 ity of the valves normal for Pentamke s are here reversed, the 

 brachial valve being the larger and deeper, with full, strongly 

 arcuate an(J incurved beak, the apex of which is concealed within 



