Review of the New York Geological Reports. 49 
Fig. 1. Pentamerus galeatus. Atrypa galeata, Daim. 2. 
Euomphalus profundus, Conran. 3. Atrypa lacunosa?  Ter- 
ebratula lacunosa of Europe. 4. Lepoerinites Gebhardit. 
It is supposed that Fig. 1 may be identical 
with the Atrypa galeatus of the Wenlock lime- 
stone. ‘The English fossil seems, from a com- 
parison of figures, to be of a more globular form, 
and to have its ribs more strongly marked, than 
the New York specimens; but these shades of 
difference are, perhaps, no more than we have reason to expect in 
the same species at distant points in their geographical range. 
The disparity in their generic names arises from the Afrypa and 
Pentamerus being distinguishable only by their internal structure, 
the latter being provided with internal vertical laminz or pro- 
jections, which give to its internal cast for a certain distance from 
the hinge five divisions, as is here represented, which are not ob- 
at ils 
Internal Casts of Pentamerus. Towa. 
servable in casts of the former. But it may be asked, may not 
this internal structure vary with the circumstances nite which 
the fossilization has taken place? Might not the internal sup- 
ports, under certain conditions, be absorbed during petrifaction 
without leaving any impress, either on the internal cast or inner 
concavity of the fossil shell? Is it not the rarest thing to find 
the spiral appendage of the Spirifer preserved? And has not its 
synonym Delthyris originated from this very cause ? 
_ Fig. 4 shows the outer and inner (?) structure of a Crinoidean 
Rte a more perfected condition in Maruer’s report, p. 346, 
and first known as the nerint istic of © 
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