164 [ Senate 



species with S. congesta. The specimen from which the latter was described 

 is a ver}- sjmnictrical and rotund form, in which the depression on the 

 mesial fold is scarcely marked ; while the surface has been in a slight de- 

 gree worn and exfoliated, so that the little granules or bases of spines arc 

 nearly obliterated, leaving a striated surface, which is in some parts can- 

 cellated by concentric lines. 



The figures 1 and 1 a represent two views of a specimen having the 

 granulations preserved upon the shell. 



Fig. 1 i is from a specimen with more extended hinge-line. 



Fig. 2 a and 2 b are views of the specimen designated S. congesta as 

 above. 



These figures, reduced in size and beautifully executed, appear in 

 Marcou's Explanatory Text, etc., pi. 3, f. 7, as S. heteroditus,J>'S.V'R.A^c. 

 It is scarcely necessary to say that this species has very little resemblance 

 to S. htteroclitus. 



Spirifer medialis. 



Delthyris medialis, Hall : Report, 4thGeol.Dist. N.Y. 1843, p. 208, f.8. 

 The figure below is of the dorsal valve entire at the extremities. 



Spirifer medialis. 



Spirifer angusta (n.s.). 



Shell extremely transverse; lateral extremities very attenuated; 

 hinge-line about four times as long as the width of the dorsal 

 valve : dorsal valve with a simple mesial fold, and about 

 fourteen or fifteen simple narrow plications on each side ; 

 beak and cardinal margin incurved : ventral valve about two- 

 thirds as wide as the dorsal valve, with a sharp well defined 



