29 



rounded striae, which are frequently increased by implantation ; these 

 are crossed by fine concentric stria3 and imbricating lines of growth, 

 the latter being numerous near the margin in the older shells. 



This species presents all the characters of Streptorhynchus, except 

 that the ventral beak is not distorted in any of the specimens exam- 

 ined, as is usual in this genus. This peculiarity, with the sub-lenticu- 

 lar form of adult shells, which is also unusual in species of this genus, 

 renders it comparatively easy to distinguish it. 



Locality and position, in limestone of the age of the Chemung 

 beds at Burlington, Clarkesville, Mo., and Hamburg, El. 



Genus Productus Sowerby. 



Productus viminalis (n. s.) Shell moderately large, thin ; 

 ventral valve much elevated in front, where it is about as wide as its 

 length, broadly rounded in front, from which it is somewhat regularly 

 arcuate at the beak ; this is rather small, prominent, and incurved ; 

 hinge line equalling, or nearly equalling, the greatest width of the 

 shell. Surface marked by numerous, somewhat rugose, tubular costEe, 

 showing the bases of tubular spines on their backs, which are more 

 numerous near the front and at the sides ; near the front margin the 

 costfe branch oif into prominent, rough, irregular fascicles. The 

 costse are crossed by fine striae of growth, and a few more or less 

 distinct concentric undulations. 



Locality and position, in the upper division of the Burlington 

 Limestone, Burlington, Iowa. 



Genus Chonetes Fischer. 



Chonetes geniculata (n. s.) Shell small, sub-oval in outline ; 

 hinge line scarcely equal to the greatest width ; dorsal valve moder- 

 ately concave, a little flattened at the cardinal extremities, not closely 

 following the curvature of the ventral valve, which in the older speci- 

 mens is very geniculate near the umbo, the beak being small, and the 

 umbonal parts flattened. Area narrow, slightly concave ; that of the 

 ventral valve about twice the width of the other, having about three 

 small spines along its outer margin, on each side of the beak ; deltid- 

 ial callosity about as wide as high. Surface marked by about forty- 

 five or fifty shghtly elevated, rounded strise, which are crossed by 

 fine lines of growth. 



Locality and position, in the Chemung beds at Burlington, Iowa 

 (?), and their equivalents at Hamburg, 111., and Clarkesville, Mo. 



Genus Crania Ketzius. 

 Crania Sheldoni* (n. s.) Dorsal valve circular or subcircu- 

 lar in outline, irregularly convex ; beak somewhat elevated, smooth, 



* Prof. D. S. Sheldon, Griswold College, Davenport, Iowa. 



