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PALAEONTOLOGY OF NEW-YORK. 
PRODUCTELLJ3 OP THE CHEMUNG GROUP. 
Prodnctella hirsuta. 
PLATE XXIV. 
Strophomena membranacea : Vakcxem, Sep. 3d Geol. Dist. New-York, p.168, f. 4 and 5. 
Not Leptcena membranacea : Phillips, Pal. Fossils, p.60, f. 101. 
Not Productus membranaceus : Hall in Tenth Report on the State Cabinet, p. 175. 1857. 
Shell semielliptical, concavo-convex : hinge-line equalling or a little 
less than the width of the shell; length and breadth about as 8 to 10 
or 12, or as 9 to 11, and, from natural or accidental causes, varying to 
length and breadth equal. 
Ventral valve convex in the middle, gibbous on the umbo, gradually 
curving to the front and lower lateral margins, and abruptly depressed 
towards the cardino-lateral margins, which are nearly fiat and broadly 
auriculate, with extremities usually rounded. Dorsal valve moderately 
- concave, flattened towards the cardinal extremities, which are always 
rounded. 
Surface marked by fine imbricating concentric striae. On the ventral 
valve there is a row of somewhat strong, diverging, nearly straight 
spines on each side just below the hinge-margin; and the entire sur¬ 
face (except sometimes the umbo and more prominent portions of the 
valve) is covered by numerous slender spines, the bases of which form 
small elongate pustules on the surface. There is some evidence of an 
extremely narrow area on the ventral valve, and of teeth-sockets in the 
dorsal valve. 
In a cast of the ventral valve, the occlusor muscular imprints are nar¬ 
row and semioval, but no distinct impressions of the divaricator muscles 
have been observed. There is doubtful evidence of the presence of hinge- 
teeth. The interior of the dorsal valve is marked by numerous fine elon¬ 
gate papillae, and towards the margin these are very closely arranged, 
giving a peculiar striated aspect to the surface (a feature more percepti- 
