132 PALAEONTOLOGY OF OHIO. 



reaching to near the front of the valve, and extending fully two-thirds 

 the width of the internal cast in its broadest part. The projections 

 which have filled the cavities beneath the plate, if existing, are not ob- 

 servable, indicating a closely appressed plate, or one not at all elevated 

 or separated from the body of the shell. The vSntral valve is character- 

 ized in the cast by the great length of the processes which have filled the 

 cavities beneath the plate, showing that the beak has been extended far 

 beyond that of the dorsal valve, and that these cavities have passed to 

 a considerable distance beyond the hinge plate. The plate has been 

 very short and thickened, as indicated by the elevation of the processes 

 above the line of the hinge when viewed in profile. The processes are 

 thin and compressed toward their apices, but near their junction with 

 the other portion of the cast are thick and expanded. 



The dorsal valve of this species resembles very much a valve of Dinobu- 

 lus, with the short triangular processes beneath the plate broken away, 

 and if found separate from the opposite valve would undoubtedly have 

 been considered as belonging to a specimen of that genus, having a very 

 deep umbonal cavity. The ventral valve differs from the corresponding 

 valve of that genus only in the greater size and cardinal position of the 

 processes filling the cavities beneath the plate. It differs from Dinobolus 

 Conradi, Hall, externally, in being elongate oval instead of transversely 

 oval. Not having seen the description of the species of Monomerella de- 

 scribed by Mr. Billings, or figures of the same, we are unable to say in 

 what particulars it may correspond to or difier from that one. The 

 structure of the valves and processes in this species would seem to tend 

 toward the union of some of these forms that have been considered as 

 distinct genera. 



Formation and locality: In the limestones of the Niagara group, at Genoa, Ohio. 

 Collection of Columbia College, New York. 



Genus MERISTINA, Hall. 

 (20th Kept. State Cab. N. Y., p. 157, 1867; Pal. N. Y., Vol. IV., p. 299, 1867.) 



Meeistina maeia, Hall. 



Plate 7, figs. 5, 6. 



Meriitella maria, Hall ; Trans. Albany Inst., Vol. IV., p. 212, 1862. 

 Meristella maria, Hall; Abstr. Trans. Albany Inst., p. 18. 

 Merisiina maria, Hall; 20th Eept. State Cab., p. 157, 1867. 

 Meristina mann, Hall; Pal. N. Y., Vol. IV., p. 299, 1867. 



The specimens of the species observed from Ohio are in the condition 

 of internal casts, and present the features of the interior of the shell 



