PRODUCTELLiE OF THE HAMILTON GROUP. 169 



Pi'oductclla subalata. 



PLATE XXIII. 



Productut tubalatus : Tenth Report on the State Cabinet, p. 174. 1847. 



" " Greological Report of Iowa, part ii, pa. 500, pi. 3, f. 10. 



Shell semielliptical or semicircular, usually much wider than high ; 

 hinge-extremities equalling or less than the width of the shell. Ven- 

 tral vajve ventricose in the middle, gibbous on the umbo and towards 

 the beak ; extended, flattened and auriculate at the hinge-extremities : 

 beak incurved over the hinge-line. There is a distinct narrow area* 

 extending for more than half the length of the hinge-line. 



The surface is marked by fine concentric striaB, with indications of radia- 

 ting striae within the substance of the shell. The cardinal margins and 

 the ears are marked by strong wrinkles which are often visible on the 

 body of the shell. The spines are variable in number, often crowded 

 together on. the ears and adjacent portions of the shell, and irregularly 

 scattered upon the middle and anterior part of the valve. 

 This species is noticed in this place from its great similarity to the P. rarispina 



of the Chemung group of New-York. The specimen figured (PI. xxiii, f. 49) is a 



ventral valve above the prevailing size, with a greater extension of the hinge-line 



than usual. 



Geological formation and locality. In the calcareous shales of the Hamilton 



group at Rock island, Illinois. , 



Productas? (sp.). 



PLATE XXin. 



A single dorsal valve, of comparatively large size, occurs with P. spi- 

 nulicosta, near Bellona in Yates county. When entire, it has had a length 

 of about one inch and a quarter, with a width of an inch and a half The 

 interior of the shell is exposed, but the cardinal process is broken ofiF, 

 and there are no teeth-sockets visible. The surface is marked by slender 

 pustuliform ridges, which become more elongate as they recede from the 

 hinge-line, and on the middle and lower part of the shell are bifurcated, 

 and show finer ridges between. 



This specimen cannot be clearly identified with any described form ; but in 

 the absence of other material, I hesitate to indicate it as a distinct species. 



Geological formation and locality. In the shales of the Hamilton group, near 

 Bellona, Yates county. , 



