No. 109.] 



179 



PeODUCTUS BOYDII (n.s.). 



Pal.N.Y. Vol.iv. 



Shell varying from semielliptical to transversely broad-oval ; 

 hinge-line usually shorter than the width of the shell, and 

 rounded at the extremities : ventral valve ranging from 

 moderately convex to gibbous in the middle and nmbonal 

 regions, marked down the centre by a shallow and sometimes 

 well-defined sinus. Surface concentrically striated and orna- 

 mented by numerous radiating lines of tubercles, which in per- 

 fect specimens are surmounted by strong curved spines ; cardinal 

 and lateral margins garnished with a row of strong curved 

 spines; vascular impression bilobed, deeply striated, reaching 

 to the middle of the shell : surface of cast finely punctate. 

 This species is readily distinguished by the strong, rather distant spini- 

 ferous tubercles, which are often arranged in distinct radiating lines ; by 

 the shallow mesial sinus in the ventral valve, short hinge-line and strong 

 curving spines. Although in form the proportions of height and width vary 

 extremely, the general surface characters are always reliable, and there 

 are no gradations which pass to other species. 



Geological position and locality. Shaly sandstones of the Chemung 

 group : Allegany county, N.Y. 







Prodxjotos botdii. 



