

of North America with those of Europe. 227 



cies of the Niagara group and that of the Delthyris shale have 

 been regarded as identical. 



The same observations apply with almost equal force to the 

 different species of Ceramus. The type of Phacops appears in 

 the Trenton limestone in the species P. Dalmani. In subsequent 

 deposits this type is numerously represented, and the forms appear- 

 ing in successive stages have not always been recognized as dis- 

 tinct species, though actually different. 



This truth applies with equal force to other classes, and though 

 the forms are less conspicuous, it becomes equally important to 

 recognize their differences or agreement. The earliest type al- 

 ways better enables us to carry forward the idea in successive 

 periods, and to refer varieties of form or species to a standard, than 

 to make ourselves acquainted with the subsequent forms which 

 have reference to that type. 



I have given in the succeeding remarks some observations on 

 several species of fossils cited in this paper, in instances where we 

 think the original may lead to erroneous opinions, or where any 

 new facts of importance have transpired. 



Bellerophon bilobatus. — Since the publication of the first vol- 

 ume of the Palaeontology of New York, two or three very imper- 

 fect specimens of a form undistinguishable from B. bilobatus. have 

 been found by Col. Jewett in the Clinton group at Lockport. 



Subulites elongate. — A second species of this peculiar genus 

 has recently been obtained near Watertown, Jefferson county, 

 New York. 



Orammysia hamiltonensis [DeVern.], ( Pterin ea bisvlrata, 

 Conrad, Ann. Geol. Report, N. Y., 1838, pa<re 116. Cyprirar- 

 dites bisulcata, Ann. Report of 1841, page 52.) This shell is 

 v ery properly separated by M. de Verneuil from any previously 

 established genus; but the name of the species, according to es- 

 tablished usage, must give place to that proposed by Mr. Conrad. 

 The species is remarkably abundant and widely extended in the 

 Hamilton group, and the figures of M. de Verneuil are very char- 



acteristic. 



T. prism, Schlot., T. qffi 



ow.) — It i s difficult to believe that the great variety of forms 

 which we find from the Clinton group to the Chemung group in- 

 clusive, are all of this species, though presenting a strong similar- 

 ity of character. We may yet hope that the discovery of sepa- 

 rated valves will enable us to detect characters, which will prove 

 l, ie well defined forms of the Niagara group and those of the 

 Hamilton group to be distinct species. 



Pottamerus oblongus, Sow. — This species though found in 

 the United States at the base of the upper Silurian stage, is regard- 

 ed in Europe as belonging to the lower stage. There can be no 

 question as to its uniform nosition in this country, and as we have 





