174 
PALAEONTOLOGY OF NEW YORE. 
in one mm. near the aperture; and in another of four mm. in length there are 
but three annulations in the length of a millimetre. In a specimen of six mm. 
in length there are sixteen annulations in the space of three mm. towards the 
larger end, and twelve in two mm. near the aperture. Several imperfect 
individuals in limestone, measuring from two to three mm. each, have from 
three and a half to four annulations in each millimetre. 
Leaving out of consideration the T. distans of the Niagara group, this is the 
only species in the rocks of New York which, so far as our knowledge extends, 
is ornamented by longitudinal stride. These striae are often obscure or indis¬ 
tinguishable by the naked eye; and this is usually true of the specimens 
occurring in the softer shales. This ornamentation, however, is often very dis¬ 
tinctly preserved on partial casts of the interior, more especially in specimens 
imbedded in compact limestone, where the outer shell is exfoliated. 
There are evidently two distinct forms or varieties of this species, one of 
which is more slender and elongate than the other. As the shorter one 
acquires the same asjiect as the longer, the condition, ajyparently, is not due 
to age. In the shorter form that portion near the aperture, with closely 
arranged annulations, is quite similar to the longer form, and the shortening 
has taken place between this portion and the smooth apical end, or in the 
space occupied by the more distant annulations. The apex is not always 
acute, hut the initial point is often a minute ovoid bulb, which appears to be 
of organic origin, and not due to subsequent influences.* 
This species differs sufficiently from all. others in rocks of the same age, to 
he readily identified, and especially where the surface-striae are fully preserved. 
Iir general form only, it. resembles the young of T. scalar if or mis, but it is 
otherwise easily distinguished, as well as from all others, in the absence of 
transverse striae. 
Formation and localities. This species occurs in the Marcellus shale, and in 
limestone associated therewith, at numerous localities, from Schoharie county 
on the east to near the shore of Lake Erie. It occurs at Cherry Valley in 
* This minute bulb is so precisely like the initial point of the shell in Balantium, and as represented in - 
the recent forms of Styliola, that I cannot doubt that it is of precisely similar character and significance. 
