198 
NAUTILOIDEA. 
half of their contour rounded and the other flattened) so noticeable 
in Huronia obliqua. This feature is not existent in D. conoideus. 
A badly preserved specimen from Niagara (formerly in Dr. Man tell s 
collection), agreeing essentially with the present species, shows re- 
mains of the septa and shell-wall. All the examples, except the 
last mentioned, are chalcedonized. 
Horizon. Niagara Group (M'enlock). 
Localities. Drummond Island, Lake Huron ; Niagara. 
Eepresented hy a few specimens, ineluding one of those figured 
by Dr. Bigshy. Some were transferred from the Museum of Practieal 
Geology. 
Discosorus gracilis, sp. nov. 
1877. Discosorus indeierminc, Barrande, Syst. Sil. de la Bolieme, 
vol. ii. Suppl^m. et S(5rie tardive, pi. cccclxxiv. ff. 9, 10. 
Fig. 26. 
Biscosonis gracilis. — A. Fragment of the septate part of the shell, the thin test 
being broken in a vertical direction, so as to expose the siphuncle to view. 
B. Internal view of another specimen cut longitudinally, showing the 
sheath, sh, and the remains of the endosiphon, en. Natural size. 
Sj). Char. Shell slightly curved. Section probably nearly circular 
in its normal condition, but compressed in one of the specimens. 
Bate of increase 1 in 3. Septa 2 lines apart at a diameter of 
7 lines ; the specimen measured is, however, somewhat compressed. 
