PALEONTOLOGY OF NEW-YORK. 3 



Dalmania and Phacops are remarkable for their spiniferous character ; 

 while the Lic;ias and Acidaspis, yet known only in fragments, are gf 

 the most extravagant forms of those genera. 



Whatever may be the ultimate decision relative to the line of separa- 

 tion between Silurian and Devonian systems, the base of the Schoharie 

 grit offers a much more decided limitation below, than does the Oriskany 

 sandstone. The new fauna bears less relation to the preceding, and many 

 of the new types are of a strikingly distinct character. In the Oriskany 

 sandstone, we have a considerable number of species which first appear 

 in the Lower Helderberg group ; and the connection between these two 

 formations is much more intimate than between the Oriskany sandstone 

 and the Schoharie grit. 



Since the faunae of the Schoharie grit and of the succeeding forma- 

 tions, more especially as far as the Hamilton group inclusive, have so 

 many features in common, I have grouped the fossils together, with a 

 view to a more perfect zoological arrangement ; and, in the first place, 

 I introduce the Brachiopoda of all these formations, designating under 

 each description, as well as in the title of the plate, the rock from which 

 they have been derived. 



In arranging the plates, I have followed to some extent the order in 

 which the fossil genera appeared in time, taking care nevertheless to 

 preserve the proper zoological arrangement. The following pages, there- 

 fore, with the accompanying plates, will present a pretty full illustration 

 of the Brachiopoda now known in these groups, before named, within 

 the State of New-York. 



I have sometimes found it necessary to go beyond the limits of the 

 State, to secure specimens fit for the illustration of species known to 

 occur within its limits; and a few extra-limital species have been intro- 

 duced for the purposes of comparison. In doing this, however, I have 

 taken great care, as I have always heretofore done, to avoid deriving 

 specimens from any portion of the country, or any State, where surveys 

 have been going on, in which a department of palajontology has been 

 organized, and whence we might have reasonable expectation of seeing 

 the fossils described and illustrated. 



