830 Repoet of the State Geologist. 



vation is situated somewhat further forward than the opposite 

 valve. A faint longitudinal septum extends a short distance for- 

 ward from the apex of the platform. Crown of the crescent 

 faint ; terminal scars as in the pedicle-valve. 



From the magnesian limestone of the Magara group, near 

 Cedarhurgh, Wisconsin, in association with Dinobolus Conradi, 

 Monomerelln prisoa and M. Greenii. 



Monomerella Ortoni. 

 Plate 2, figs. 4, 5. 

 Monomerella Ortoni, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 175, 

 pi. ivc, figs. 14, 15. 1892. 



Pedicle-valve large, with a high cardinal area, which is gently 

 incurved longitudinally and crossed by lamellose growth-lines, 

 upon which the evidences of the deltidial ridges are extremely 

 faint or altogether wanting. Umbonal cavities conspicuous, but 

 much shorter than is usual in M. jprisoa. Cardinal slope large, 

 triangular and divided by an axial furrow. Cardinal buttress 

 broad at the base but not especially prominent. Platform appar- 

 ent only at its anterior QdgQ where it has a broad anterior slope. 

 Crescent well defined beneath the hinge-line ; terminal scars very 

 prominent ; central, lateral and anterior impressions discernible on 

 the platform. Pallial sinuses very strong, the outer ramifications 

 from which are distinctly seen. Brachial valve unknown. 



From the Niagara dolomitic limestone, at the Rising Sun 

 quarries, Wood county, Ohio. 



Monomerella Egani. 



Plate 2, fig. 3. 

 Monomerella Egani, Hall. Palaeontology of N. Y., vol. VIII, pt. 1, p. 175, 

 pi. ivc, fig. 16. 1893. 



Brachial valve with an unusually high cardinal area, indicating 

 a quite elevated beak. This area is strongly striated trans- 

 versely, and bears two faint longitudinal depressions correspond- 

 ing in position to the deltidial ridges of the pedicle-valve. It is 

 continued laterally nearly to the middle of the margins. Cres- 

 cent very narrow over the crown, lying close upon the cardinal 

 line ; at its turn forward it is developed into a deep, narrow, 

 elongate muscular scar, which is continued into a broader ter- 

 minal impression. Platform sharply elevated at its anterior 



