174 [Senate 



PrODUCTUS EXAKTHEMATUS (n. S.)- 

 Pal. N.Y. Vol. iv. 



Shell semioval; hinge-line scarcely equalling the greatest width 

 of tlie shell : dorsal valve o]ie-third wider than high, slightly 

 concave, entire surface pustulose. 



A single valve only of this species has fallen under my observation ; but 

 the characters are so distinct from either of the other species, that I cannot 

 hesitate to separate it from them. 



A specimen from Bakeoven, Illinois, occurring in limestone of the age 

 of the Hamilton group, is very similar if not belonging to this species. I 

 presume it to be the one referrq^ by Messrs. Norwood and Pratten 

 to P. suhacvJeatus; while another form, with elongated pustulose ridges, 

 is probably the one referred by the same authors to P. murchisonianus. 

 The spiniferous ridges in the latter species are often continuous for more 

 than half the length of the shell above the base, in which character it is 

 similar to P. spinuUcosics ; but the absence of an area, as well as other 

 characters, render it impossible to regard either of these as identical with 

 p. murchisonianus. 



Geological positio7i and locality. Shales of the Hamilton group : Shore 

 of Seneca lake, Ontario county. 



Productus subalatus. 



Pal. N.Y. Vol. iv. 

 Productus subalatus, Hall : Iowa Geol. Report, 1857. 



Shell semielliptical, with the cardinal extremities alate : ventral 

 valve gibbous in the middle, depressed in front, and much ex- 

 panded laterally towards the cardinal extremities ; beak abruptly 

 incurved, the umbo projecting above the hinge-line j the cardi- 

 nal margin marked by more or less distinct folds or wrinkles, 

 becoming obsolete on the middle of the shell, which is crossed 

 by irregular or undulating concentric striee. In some individuals, 

 indistinct longitudinal strige are visible. Surface ornamented by 

 numerous strong rounded tubular spines, the bases of which 

 remain irregularly distributed. Some well preserved specimens 

 show a distluct row of spines near the cardinal margin, while 



