SPIRIFERiE OF THE CHEMUNG GROUP. 
251 
allied-to S. pseudolineata of the Keokuk limestone. The specimens of S. 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 8. pseudolineata, 
S. hirtus , and 8. prmmaiura. 
This species is associated with great numbers of 8. disjuncta, Streptorhynchus 
chemung ensis var. pectinacea , Pro ductus lachrymosa var., Chonetes muricata, C. 
setigera , and a Chonetes with about fifty fine striae, 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 Spirifera 
disjuncta. 
Some important considerations are suggested by the study of Spirifera prcemor 
tura, Spirifera alta , and their associates. 
The species which I have here designated as Spirifera prcematura exhibits no 
external markings which enable one to say that it is distinct from 8. 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 those 
in the western locality; but still among the more conspicuous of these is Spirifera 
alta, Productus 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 
species in the rocks of the West and Southwest which are usually referred to a 
