166 PALEONTOLOGY OF NEW-YORK. 



PRODUCTELL^ OP THE CHEMUNG GROUP. 



Productella liirsata. 



PLATE XXIV. 



Stropkomena membfanacea : Vanuxem, Ucp. 3d Geol. Dist. New-Tork, p. 1C8, f. 4 and 6. 



Not Lejilana membra nacca : PHiLLirs, I'al. Fossils, p. GO, f. 101. 



Not Produttui mtmbranaceiu : Hall in Tenth Report on the Stat« 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 flat 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- 



