23 



from the base ; transverse ridges forty-five or fifty to the inch, finely 

 nodose, sweeping downward with gentle curves to the central depres- 

 sion, where they meet with a very obtuse, rounded angle, and cross 

 with little interruption, except where they slightly alternate ; spaces 

 between them smooth; grooves at the salient angles distinct, at which 

 the ends of the transverse ridges regularly alternate, having a small 

 pit at the end of each, giving the appearance of a finely-stitched suture. 



Partially decomposed fragments of this species have been observed 

 in small concretionary masses, having the appearance of coprolites, 

 indicating the probability that they were the vi(itims of the fishes whose 

 remains are frequently found in the same strata. 



Locality and position, in the upper division of the Burlington Lime- 

 stone, Burlington, Iowa. 



Brachiopoda. 

 Genus Rhynchonella Fischer. 



Rhynchonella caput testumnis (n. s.) Shell large, subtrian- 

 gular, subcuneate, front rather fully rounded, meeting the lateral slopes 

 at an obtuse angle ; sides somewhat concave, free from plications near the 

 beaks, and sloping to them with gentle incurvatures, giving the shell 

 an angular appearance about the beaks, which are small, and at which 

 the sides meet at an acute angle ; both valves regularly and nearly 

 equally convex ; dorsal beak closely incurved beneath the ventral beak, 

 which is slightly incurved. Foramen and deltidium unknown. Sur- 

 face marked by from sixteen to eighteen distinct, somewhat rounded 

 plications on each valve, which mostly reach the beak with some dis- 

 tinctness, but are occasionally increased, both by implantation and 

 bifurcation. These are traversed by fine radiating lines, and crossed 

 by fine concentric lines of growth. 



Mesial fold and sinus scarcely defined, but the front is slightly 

 emarginate in the older specimens, by the elevation of the lingual 

 extension of the lower valve with a gradual curve, which includes 

 five or six of the plications. 



Locality and position, at the base of the Burlington Limestone, 

 Burlington, Iowa. 



Rhynchonella Ottumwa (n. s.) Shell rather small, variable in 

 form, somewhat triangular, subpentagonal or subovoid in outline ; 

 valves subequally convex ; ventral valve regularly convex along the 

 centre from beak to front, broadly convex across the centre from side to 

 side ; beak rather large, long, projecting much backward, pointed, and 

 curving upward with rather more than the regular curvature of the 

 valve, the space beneath it a little flattened, giving somewhat the ap- 

 pearance of an area ; deltidial plates occupying a rather large, equi- 

 lateral triangular space, with a moderately large, oval foramen. Dor- 



