PRODUCTELL^ OF THE CHEMUNG GROUP. 169 



Productella boydii. 



PLATE XXIV. 

 Productus boydii : Hall in Tenth Report on the State Cabinet, p. 179. 1857. 



Shell of medium size or larger, transverse, varying from semielliptical 

 to broad-oval from the rounding of the cardinal extremities ; cardinal 

 line less than the width of the shelL 

 Ventral valve varying from moderately convex to gibbous in the middle 

 and towards the umbo, with a more or less defined mesial depression 

 extending from the umbo to the front of the shell, which is sinuate, 

 somewhat gently curving to the front and taso-lateral margins, abruptly 

 depressed on the cardino-lateral slopes, and extended into wide ears 

 which are more or less distinctly rounded at the extremities. 

 Dorsal valve moderately concave, with a distinct longitudinal mesial 

 elevation corresponding to the depression of the ventral valve, and 

 giving the basal margin a sinuate outline. Cardinal extremities round- 

 ed, and the cardinal line much shorter than the width of the shell. 

 Surface concentrically, striated, and marked by numerous elongate pus- 

 tuliform spiniferous ridges supporting slender elongate spines, while 

 there are one or two rows of stronger curving spines on the ears. The 

 interior of the dorsal valve is marked in like manner by pustuliform 

 nodes, indicating fossets on the exterior surface, which sometimes 

 have their length transverse to the shell, or producing short transverse 

 wrinkles. In some specimens, faint radiating striae mark the surface of 

 the shell. 



The casts of the ventral valve show the marks of the occlusor mus- 

 cles near the apex on each side of the mesial depression, which, on the 

 interior of the shell, would be an elevated ridge. The divaricator muscu- 

 lar impressions are deeply striated, wide and spreading, extending nearly 

 to the middle of the length of the shell. The interior of the dorsal valve 

 shows a narrow mesial septum, but the cardinal process has not been 

 determined. The whole interior surface is papillose or punctate. 



[ PALiEONTOLOGT IV.] 22 



