450 PROCEEDINGS OF THE ACADEMY OF 



MOLLUSCA. 



BRACHIOPODA. 



Genus CHONETES, Fischer. 



Chonetes planumbona. Shell of medium size, nearly semicircular ; length 

 from two-thirds to three-fourths the breadth ; hinge line about equalling the 

 greatest breadth ; front rounded, or forming with the sides a nearly semi- 

 circular curve ; lateral margins intersecting the hinge at right-angles, or 

 sometimes very slightly sinuous near the ears. Ventral valve gibbous, most 

 convex in the middle, and flattened at the umbo, destitute of any traces of a 

 mesial sinus ; ears a little compressed ; cardinal margin sloping slightly from 

 the beak, on each side of which it is armed with five or six spines ; area of 

 moderate breadth ; foramen broad, triangular, the upper angle being rounded. 

 Dorsal valve concave, or following nearly the curve of the other valve ; cardinal 

 process moderately prominent, nearly or quite closing the foramen of the 

 opposite valve ; interior without a prominent mesial ridge, rather distinctly 

 granulose, the granules being arranged in radiating lines ; visceral scar rather 

 large ; impressions of aductor muscles small and deep. Surface of both valves 

 apparently smooth or only marked by obscure undulations of growth, but 

 showing under a lens nearly obsolete traces of depressed rounded radiating 

 striae, crossed by minute concentric lines or wrinkles. 



Length 0*42 inch ; breadth 0-49 inch; convexity 0-16 inch. 



Locality and position. Monroe County, Illinois. Keokuk Limestone of 

 Lower Carboniferous series. 



Genus PRODUCTUS, Sowerby. 



Pkoductus nanus. Shell very small, nearly hemispherical ; hinge about 

 equalling the greatest breadth ; anterior side regularly rounded ; sides 

 intersecting the hinge nearly at right-angles. Ventral valve gibbous, without 

 any traces of a mesial sinus ; ears triangular, convex, and moderately distinct 

 from the swell of the visceral region ; umbo convex, incurved, and apparently 

 extending slightly beyond the hinge line. Surface ornamented by compara- 

 tively large, rounded, radiating costse, which more than equal the depressions 

 between, on the convex part of the valve, but decrease in size, and become 

 more numerous by division, and the implantation of others between, around 

 the anterior slope ; crossed by numerous very fine concentric striae, only visible 

 under a lens. The visceral region is also marked by moderately distinct 

 rather regular wrinkles, while the bases of a few scattering spines are seen 

 on the anterior slope. (Dorsal valve unknown.) 



Length 0-37 inch ; breadth 0-45 inch ; convexity 0*25 inch. 



Locality and position. Jefferson County, Iowa. Lower Coal measures. 



Peoductus paevus. Shell rather small, nearly hemispherical, without any 

 traces of a mesial sinus ; length and breadth nearly equal ; hinge about 

 equalling the greatest breadth ; front rounded ; sides sometimes slightly 

 sinuous near the ears. Ventral valve gibbous, regularly arched, not depressed 

 in the visceral region ; beak incurved a little beyond the hinge ; ears small, 

 convex, nearly rectangular at the extremities of the hinge, moderately distinct 

 from the swell of the umbo. Dorsal valve deeply concave, particularly in 

 the middle and towards the beak. Surface of both valves ornamented by 

 numerous small, rounded, rather closely arranged, occasionally bifurcating 

 strise, about six of which may be counted in the space of one-tenth of an inch. 

 Spines erect, apparently confined to the ventral valve, each ear of which 

 supports some seven or eight, while there are usually about three times that 

 number scattered around the anterior and lateral slopes. Sometimes very 



[Oct. 



