168 PALAEONTOLOGY OF NEW YORK. 



The specimens attain the length of one inch, rarely more, and usually 

 gonuwliiit less. The longest one observed has a length of nearly one inch and 

 a quarter. 



This form is stronger and more robust than any of the species of the 

 Hamilton and Chemung groups. It differs from the T. bellulus in having the 

 annuliitions of the distal portion more obtuse, while, in the Hamilton species, 

 the apical portion with fine annulations is proportionally longer and more 

 attenuate, and- the entire length in the longest individual is greater. In T. 

 bellulus the annulations on the large part of the tube are more acute, the 

 intermediate depressions are proportionally wider, and the transverse striae 

 somewhat stronger. T. scalariformis differs in the same manner from T. elon- 

 gatus of the Lower Helderberg group, which has thin, sharp annulations, and 

 a more gradually attenuate form. 



In the usually macerated condition of most of the specimens, the transverse 

 striaj are chiefly obliterated, and it is only in rare individuals that these 

 markings are well preserved. The same influence has subdued the sharpness 

 of the annulations, and in many examples this cause, together with the effects 

 of subsequent pressure, has given them a subnodose character. 



In the compact limestones of New York and of Sandusky, Ohio, the exterior 

 surface is rarely well preserved, and it is only on some slabs of a thinly 

 laminated and often argillaceous limestone that the full form and external 

 characters have been retained. 



Formation and localities. This species occurs in the Upper Helderberg lime- 

 stone at Schoharie in eastern New York, and at Le Roy and other points in 

 the central part of the State. It is abundant in the same limestone near 

 Sandusky and at Delaware, Ohio, and at Charlestown, Ind. It likewise occurs 

 as casts of the interior, or sometimes partially preserving the shell, in a sand- 

 stone at the base of the Corniferous limestone at Pendleton, Indiana. The 

 known geographical extension of the species is therefore at least seven hundred 

 miles, and it seems quite probable that it will prove coextensive with the 

 limestone formation of the Upper Helderberg group. 



