PTEROPODA. 
161 
The T. arenosus has only been found in a single locality in the Helderberg 
range in the town of Knox, Albany county, N. Y. 
The T. scalariformis is rare at Schoharie, and has been found in two localities 
in central and western New York. It seems to be the nearest representative 
of the T. scalaris of Europe which we have in this country, judging from all the 
figures of that species accessible to me, and it may be only a geographical 
variety. The form indicated as T. sicula is identical with T. scalariformis, so 
far as can be determined from the condition of the New York specimens, 
and, while rare in this State, is extremely abundant in the neighborhood of 
Sandusky and Delaware, Ohio. It also occurs in Charlestown and Pendleton, 
Indiana. 
The T. attenuatus is very abundant in some decomposing arenaceous shales 
in Otsego county, N. Y., and T. bellulus occurs in several localities in the central 
part of the State; but neither of them are known to me as occurring in the 
western counties, or in any localities of the Hamilton group beyond the limits 
of New York in a westerly direction. On the other hand, the T. attenuatus is 
extremely abundant in some arenaceous beds of the Hamilton group at 
Saddleback Ridge, in Huntington county, Pa.; a point at least three hundred 
miles southward from the localities in the State of New York. 
The T. spiculus of the Chemung group is very numerous in certain decom¬ 
posing layers to the south of Ithaca, and in Cortland county, N. Y.; but no speci¬ 
mens have occurred in all the extensive collections made in the country west 
of the Genesee river, nor in all the southern range of counties of the State. 
The Devonian species, T. Hoyti of White, and T. subtilis, described by 
Winchell, we know only from the localities cited by their authors. 
Of the species from the rocks of Lower Silurian age, we have no other 
knowledge of their geographical distribution than as given by their authors, 
who cite the occurrence of the species in three localities in the State of Illinois 
and one in Indiana. 
From our present knowledge, therefore, we might conclude that the distri¬ 
bution of the species is very unequal; but it is more probable that our 
collections are too incomplete to admit of any satisfactory generalization at 
21 
