CEPHALOPODA. 811 
Gyroceras duplicicostatum.] 
venter they are curved forward into a broadly angled saddle, which is not acu te, 
but is sharper on the septa nearest the aperture. The depth of the air-chambers 
on this side is about one-half greater than onthe dorsum. The form of the suture 
is so characteristic that, taken in conjunction with the form of the shell, I have 
ventured to regard the specimen as representing a new specific form. 
Dimensions. Length, 80 mm.; major axis of apertural end, 16 mm.; minor axis 
12-5 mm.; major axis of distal end 12 mm.; minor axis, 10 mm. Average depth of 
air-chamber on venter, 2 mm.; on dorsum, 14mm. 
Formation and locality.—In the lower blue beds of the Trenton limestone at Janesville, Wisconsin. 
Museum Register, No. 62. 
Genus GYROCERAS, DeKoninck, 1841. 
GyrocEeRas DupLicicostatum Whitfield, 1878. 
Gyroceras duplicicostatum WHITFIELD, 1878. Ann. Rept. Geol. Sury. Wisconsin for 1877, p. 78. 
Gyroceras duplicicostatum WHITFIELD, 1882. Geology of Wisconsin, vol. iv, p. 235, pl. vu, fig. 1, 
Fragments of this species occur in specimens in the state museum, collected 
from the lower blue beds of the Trenton limestone at Janesville, Wisconsin. The 
original specimens were from the Trenton at Bristol and Beloit, in that state. 
Family TASNOCERATID A. 
Genus EURYSTOMITES, Schroeder, 1891. 
Eurystomites unpatus Hmmons, 1842, var. occripenTaLis Hall, 1861. 
Lituites undatus, var. occidentalis HALL, 1861. Rept. Supt. Geol. Surv. Wisconsin, p. 38. 
This well known form is represented by several specimens in the collections 
before me, some of them of large size, all possessing the broad whorls with flattened 
dorsum and the simple concave septa characterizing the western variety of this 
species. The New York specimens upon which the species was founded, seem to 
be restricted in range to narrow limits within the Black River limestone formation 
but the specimens from Minnesota indicate a more general distribution. Two 
large examples have a diameter of about 140 mm.; smaller specimens show the 
extreme ventral but submarginal position of the sipho and the dorsal depression or 
groove on each whorl made by contact with that next within. 
The species has usually been referred to the genus Lituztes, Breyn, the type of 
which is Litwites lituus. It is evident however that the species is not a Lituwites, and 
and I have here followed the recent suggestion of Hyatt* that it be placed with 
Kurystomites. 
Formation and locality.—In the Trenton limestone at Minneapolis, Spring Valley, Northfield, Pine 
Island, Minnesota;.Dixon and Rockton, Illinois. 
Museum Register, Nos. 5066,5714. 
* Proc. Amer. Philos. Soc., vol. xxxii, p. 445. 1894. 
