30 



inclined backward, and situated near the posterior margin. Surface 

 marked by numerous distinct, fine, somewhat rugose striae. Ventral 

 valve unknown. 



This species bears some resemblance to C. crenistriata Hall, of the 

 Hamilton group of New York, but is distinct from that in the charac- 

 ter of the strife, the convexity of the ventral valve, and the position of 

 its beak. 



Locality and position, in Calcareous Shales of the age of the Hamilton 

 group of New York, New BuflFalo, and Iowa City, Iowa. 



Crania keposita (n. s.) Shell varying from subcircular or subel- 

 liptical to transversely subquadrate in outline ; interior of ventral or 

 attached valve having a narrow, continuous elevation around the mar- 

 gin ; adductor muscular impressions distinctly elevated, the anterior 

 pair close together, and situated a little back of the centre ; the poste- 

 rior pair situated near the posterior margin, and about as far apart as 

 their distance from the anterior pair. 



The only specimens of this species discovered are attached, by the 

 full breadth of the ventral valve, — the dorsal valve absent, — to a 

 valve of Spirifer Grimesi. 



Genus DisciNA Lamark. 



DisciNA CAPAX (n. s.) Shell subcircular in outline, dorsal valve 

 much convex, apex small, prominent, eccentric, and pointing back- 

 wards. Surface having a rather smooth appearance, but marked by 

 fine lines of growth, and these crossed by very faint, somewhat dis- 

 tinct, radiating striae. 



This species bears some resemblance to D. Vanuxemi, Hall, of the 

 Lower Helderberg group of New York, but differs in the more 

 eccentric position of the apex and the character of the surface- 

 markings. 



Locality and position, in the sandstone of the Chemung beds at Bur- 

 lington, Iowa. 



Genus Lingula Bruguiere. 



LiNGULA Halli* (n. s.) Shell elongate, oval in outline, about twice 

 as long as wide ; valves not very gibbous ; beaks small, prominent. 

 Surface marked by fine striae of growth ; yet its appearance is usually 

 smooth and bright. 



It most nearly resembles L. Spalula Hall, of the Genessee Slate of 

 New York, but differs in being proportionally shorter, and narrower 

 near the beaks, and has a smoother surface. 



Locality and position, in the upper and lower divisions of the Bur- 

 lington Limestone, Burlington, Iowa. 



*B. J. Hall, Esq., Burlino'ton, Iowa. 



