68 
NAUTILUIDEA. 
Remai'liS. This species closely resembles G. consohriaum, de Kon., 
but it differs from the latter by the greater number of its longitu- 
dinal ridges, and also by the form of tlie ventral side, which is much 
more excavated. 
Horizon. Calcschiste de Tournai (Assise i. e) = Carboniferous 
Limestone. 
Localitij. Tournai, Belgium. 
Bepresented in the Collection by two examples. 
Subgenus AIPOCERAS, Ifyatt h 
{Gijroceras, de Kouinck, 1880^.) 
This subgenus was instituted by Hyatt for the reception of a 
remarkable species described by de Koninck, which diticrs from 
Guroccras proper in its much more rapid rate of tapering and its 
Fig. 6. 
Gyroccras {Aipoceras) comjpressiim. — a, latoal riew, showing some of the sepia ; 
b, front view. Drawn from a specimen in the Collection. One hall 
natural size. 
subangular section, in which the ventral (convex) side forms the 
apex of the triangle, and the dorsal the base. The whorls are 
not in contact. The septa are moderately distant and the siphuncle 
^ Proc. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 296. 
^ Faune du Calcaire Carbonifere de la Belgique (Annales du Mus. Boy. 
d’Hist. Nat. de Belgique, tom. v.), p. 6. 
