174 PALAEONTOLOGY OF NEW YORK. 



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 striae. 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 aspect as the longer, the condition, apparently, 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, but 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 

 be readily identified, and especially where the surface-striae are fully preserved. 

 In general form only, it resembles the young of T. scalariformis, 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 Balantmim, and as represented in 

 th<- recent forms of Styliola, that I cannot doubt that it is of precisely similar character and significance. 



