} 10 [Senate 



MEGAMBONIA LYONI (n.s.). 



Shell obliquely subovoid, bro[idly rounded in front and on the base, sloping pos- 

 teriorly and rounded on the postero-basal margin : beak incurved and pointing 

 forward. Surface marked by flattened radiating striae, which arfe sometimes 

 dichotomized. 



The right valve shows two strong teeth just anterior to the beak, but the cha- 

 racter of the hinge-line is not ascertained. 



The shell has the form of Ambonychia; being more robust than A.carinatay 

 and with finer radiating striae, in this respect approaching A. bellastriata. The 

 presence of teeth in the hinge removes this fossil from Edmondia, to which genus 

 I should otherwise have referred it. 



Geological formation and locality. In the compact limestone of the Goniatite 

 beds; at Rockford, Indiana. 



CYPRIOARDIA VENTRICOSA ( n.s.). 



Shell subovoid, ventricose, inequilateral; hinge-line equalling little more than 

 half the entire width of the shell; umbones much elevated; beaks incurved; 

 anterior end short and abruptly rounded, lunule cordiform; ligamental area 

 strongly marked; posterior end subtruncate; umbonial slope angulated, and 

 extending to the postero-basal margin : the surface between this ridge and the 

 anterior end marked by strong concentric ridges, while the posterior concave 

 slope is nearly smooth. 

 This is a small strong shell, about three-fourths of an inch long and half an inch 



high. The depressed posterior slope occupies one-third the superficies of each valve. 

 Geological formation and locality. In the limestone with Goniatites rotatorius 



and other fossils, at Rockford, Indiana. 



Besides the preceding, there are a few other lamellibranchiate shells : one of 



these is a Nucula, resembling N'. bellatula of the Hamilton group, but smaller, 



and with more angular beaks. 



ANATINA LEDA(n.s.). 



Shell oblong, ovate, subcuneate, scarcely gibbous : anterior end rather sharply 

 rounded; posterior end produced. Anterior cardinal slope short and slightly 

 curving; posterior slope straight; basal margin curving from the anterior end 

 regularly to the posterior extremity of the cardinal line. Beak thin, pointed, 

 and but little deviated above the hinge-line. 

 This shell resembles ^. attenuata of M'Oot, but is a narrower shell, and has 



the general form and expression of Leda, but the hinge-line is not crenulated. 

 Geological formation and locality. In the Goniatite limestone : at Rockford, 



Indiana. 



NUCULA HIANS(n-s.). 



Shell ovate, gibbous, subcuneate; anterior end somewhat obliquely truncate; 



posterior side twice as long as the anterior, subacutely rounded and gaping at 



the extremity; beaks elevated, a little compressed. 



In the cast there is a depression on each side at the shorter end of the valves, 

 extending from just above the muscular imprint towards the beaks. The ( posterior) 

 anterior muscular impression is almost terminal, with a small secondary muscular 

 pit near the cardinal line : hinge crenulate. 



Geological formation and locality. In the Goniatite limestone; at Rockford, 

 Indiana. 



