No. 109.] 175 



those nearest the beak are small, and actually upcii the edge of 



the shell, as in Chonetes. 



The characteristic features of this species are the great expansion on the 

 hinge-line, and the auriculate or alatc cardino-latoral margins; also the 

 strong, round spines, without ridges or tubercles. 



In some specimens, the spines near the beak and umbo are distributed 

 somewhat regularly in radiating lines. The number of .spines varies from 

 ten or twelve to thirty or forty; and it i.s only in rare instances that they 

 are preserved near the beak. 



Geological positioii and locality. Shales of the age of the Hamilton 

 group : Rock Island, Illinois, and various localities in Iowa. 



Productus hirsutus (n.s.). 



Pal. N.Y. Vol. iv. 



Strophomena mcmbranacea, Vancxem : Rep. 3d Geol. Dist. N.York, p. 178, 



f. 4 and 5. 



Not Productus membranaceus, Von Bucii. 



Leptana mcmbranacea, PniLLirs. 



Shell semielliptical, often oblique ; hinge-line usually a little 

 longer than the greatest width of the shell : ventral valve 

 moderately gibbous, with cardiuo-lateral extremities not dis- 

 tinctly separated from the body of the shell, expanded with a 

 marginal or submarginal row of strong spines. Surface concen- 

 trically striated and covered by closely arranged, delicate, 

 hair-like spines, except a small space on each side of the 

 umbo, wdiich is sometimes destitute of these appendages. 

 This species has the ears less distinctly separated from the body of the 

 shell than P. lachrymosa, and the hinge-line more extended. It was 

 identified by Mr. Vanuxem with the european P. memhranacca; and the 

 shell, with the spines removed and preserving the strong concentric stria^ 

 has a membranaceous texture. In its slender spines it resembles P. mur- 

 chisonia, but the greater extension of the hinge-line, absence of area and 

 more closely arranged spines are marked differences. The interior of the 

 ventral ( dorsal ) valve differs most extremely from the figure given by 



DE KONINCK. 



