SPIRIFER^ OF THE CHEMUNG GROUP. 251 



allied to S. pseiidoUneala of the Keokuk limestone. The specimens of 8. hirtus in 

 my possession are very imperfect, and do not afford fair means of comparison; but 

 I am much inclined to the opinion that an examination of a larger number of the 

 Burlington species with ours will prove them identical. Both are known to me 

 only in casts, and those from the western locality do not offer sufficient grounds for 

 a satisfactory specific distinction. I shall nevertheless indicate this as distinct for 

 the present; hoping to obtain material to show the identity of S. pseudolineata, 

 S. hirtus, and 8. proBinatura. 



This species is associated with great numbers of 8. disjuncta, Streptorhynchus 

 chemnngensis var. pectinacea, Productus lachrymosa var., Chonetes muricata, O. 

 setigera, and a Chonetes with about fifty fine strise, with regular intermediate 

 puncta as in C. illinoisensis. 



The lower line of figures on Plate xxxn are of this species in its condition of 

 casts, the smaller one partially retaining the shell. 



The small figure above (fig. 32) is the ventral valve of a young individual, having 

 the beak unusually extended and the concentric undulations strongly marked. 



Figures 32 and 33 are dorsal valves of this species. 



Figures 34 and 35 are the casts of ventral valves, showing, in the space between, 

 the dental plates and extent of muscular impression. 



Geological formation and locality. In the Chemung group at Meadville, Pa., 

 and among specimens lately received from Oil Creek, associated with 8pirifera 

 disjuncta. 



Some important considerations are suggested by the study of Spirifera prcBma- 

 tura, Spirifera alta, and their associates. 



The species which I have here designated as 8pirifera prematura exhibits no 

 external markings which enable one to say that it is distinct from 3. hirtus of the 

 sandstones at Burlington, Iowa; nor does it present differences from 8. pseudo- 

 lineata which may not be reconciled with geographical influences, and with a 

 habitat nearer to the shore line and the essential absence of calcareous matter in 

 the sediments deposited. Its associates, however, are of different species from thoso 

 in the western locality; but still among the more conspicuous of these is 8pirifera 

 alta, Prodiwtus lachrymosa var., and Chonetes muricata, which have a carboniferous 

 aspect; and were it not for the presence of Spirifera disjuncta and one or two 

 others, the general aspect of the fauna might be termed carboniferous. 



If again we look at the characters of Spirifera alta, an analogue or representa- 

 tive of Spirifera cuspidata, we have many points of similarity with one or more 

 epecies in the rocks of the "West and Southwest which are usually referred to a 



