ARCTIC ORDOVICIAN AND SILURIAN CEPHALOPODS 277 
specimen is numbered 802 B in the American Museum of Nat- 
ural History in New York city. 
Remarks. — The general aspect of the shell with its promi- 
nent ribs and broad intermediate grooves is so similar to that of 
Kionoceras that the generic reference may be assumed to be 
correct. Compared with Kionoceras kentlandense Kindle and 
Breger, from the Black River of northwestern Indiana, the 
number of vertical ribs is only 2 or 3 less, their number in the 
Indiana species being 22 or 23. It is probable that the New 
York Trenton species is distinct from the Indiana Black River 
form, but in case of the former the interior structure is unknown 
and in case of the latter the surface features are not preserved. 
A specimen similar to the New York species in the number 
and prominence of its vertical ribs occurs in the Leray member 
of the Lowville at Pauquette Rapids, in Ontario. There are 
22 ribs, and the cross-section is cylindrical. It is 21 mm. long, 
and enlarges from 3.6 mm. to 4.7 mm. in this length. The 
siphuncle is half a millimeter in diameter, and its position is 
almost central . 
13. Kionoceras kentlandense (Kindle and Breger) 
Orthoceras (Kionoceras) kentlandensis Kindle and Breger, 
28th Ann. Rep. Dep. Geol. Nat. Res. Indiana, 1904, p. 470, 
pi. 21, fig. 2. 
Type. — The specimen enlarges from 7 mm. at the lower end 
to 11 mm. at the upper end, the interval being 78 mm., sug- 
gesting an apical angle of 3 degrees. Only the cast of the 
interior of the conch is at hand. This is marked by 22 or 23 
vertical ribs which are distinct, though low, along the entire 
length of the specimen, including the living chamber. At the 
top of the phragmacone there is a series of 6 camerae successively 
shorter in length, indicating that the specimen had attained 
maturity; all 6 of these camerae occupy a total length equal to 
only ten-ninths of the diameter of the conch. Of the living 
chamber a length of 17 mm. remains, but this does not include 
the upper part of the living chamber which, in this genus, should 
