14 
PALAEONTOLOGY OF NEW-YORK. 
some localities in Canada, especially bordering the north side of the St. 
Lawrence and Lake Ontario*. 
We shall, probably, yet find it convenient to indicate several subordinate 
divisions in the Trenton limestone, where that rock is best developed, 
marked by the prevalence of certain species, and the almost entire re¬ 
striction of these species within narrow limits. 
The group of strata known as the Hudson-river group, which in its 
more extended signification may include all the beds from the Trenton 
limestone to the Shawangunk conglomerate, has afforded in New-York 
but small additions to the number of fossils previously known in this 
formation. From the metamorphic slates of this group on the western slope 
of the Green mountains in Vermont, we have three or more species of 
trilobites, which are of much interest, being representatives of a genus 
but little known in this country. The slates of the same age farther to the 
south have yielded some additional new species. 
* In some parts of Canada the fossils of the Trenton limestone are completely silicified; and the shells 
thus preserved are often weathered out so as to show their characters of hinge, etc. almost in the same 
perfection as in modern shells. The same result is accomplished by dissolving away the limestone by acids, 
leaving the silicified shell entire. In this manner specimens have been obtained, showing the characters of 
hinge and teeth, in Tellinomya , Modiolopsis, Ambonychia and others. These characters are such as to 
leave no doubt regarding the true relations of these fossils. 
The Genera Tellinomya and Modiolopsis have been referred by M. D’Orbigny to Lyonsia, and the 
species arc placed under that genus in his “ Prodrome de Paleontologie.” The distinctions between these 
genera were originally founded, chiefly, upon external characters; but we now have the means of showing 
the internal characters of these shells, which prove them not only entirely distinct, but in both instances 
widely different from Lyonsia. The former proves to be closely allied to Nucula (and will include several 
species previously arranged under that genus); all the species examined having a continuous series of 
crenulations along the hinge line, and an external ligament, while the species of Modiolopsis have no serial 
teeth or crenulations of this kind in the hinge. 
The Genus Ambonychia , regarded by M. D’Orbigny as equivalent to Posidonomya of Bronn, proves 
to be quite as distinct from the latter as Tellinomya is from the former. 
In the mean time, a writer, professing to give an account of the present state of American geology, has 
copied the list of fossils from the work of M. D’Orbigny (acknowledging his indebtedness to that author 
for a corrected list of American fossils) , entirely regardless of the relations of these and other fossil 
genera; and, obtaining possession, without authority, of illustrations made for the author’s own work, he 
has carelessly used them to propagate these false impressions concerning the fossils of the rocks of New- 
York and the United States. But for this circumstance, the present writer would not have animadverted 
upon the jumbled production which its author has had the self-complacency to designate by the com¬ 
prehensive title of “ American Geology” ! 
