182 
NAUTILOIDEA. 
In other species, again, the presence of the lobe is due, in part at 
least, to the sulcation of the periphery. 
‘‘The flattening of the periphery mentioned by Hyatt as also 
one of the characters of Grypoceras is not always accompanied by 
‘ V-shaped ventral lobes,’ Nautilus Picteti^ Oppel, having a flattened 
and sulcated periphery, but no ventral lobe. The distinction, there- 
fore, between Grypoceras and Hercoglossais, very difficult to maintain. 
“We include also in Hercoylossa the genus Enclimatoceras of 
Hyatt type E. Ulrichi, White {Foord and G. C. Cnch'^) 
Another group closely allied to Hercoylossa, is that which has l)een 
described (provisionally) by Mojsisovics under the name of Cly do- 
nautilus of which he has given the following description : — 
Involute high-mouthed forms with closed, or very small umbilicus, 
and three sharply-rounded lobes [in the sutures] on the sides of the 
shell, of which two are much nearer the periphery than the remain- 
ing one. In more advanced age the external (peripheral or ventral) 
lobe is divided by a large saddle-shaped median projection into two 
separate parts. There is no internal lobe. The siphuncle may be 
either above or below the centre. The surface of the shell is either 
reticulated or provided with faint lateral folds or fine ridges. 
Besides Clydonautilus Noricus^ [the type], the following species 
are included in this genus, viz. : — 
Clydonautilus Quenstedti, F. von Hauer ^ 
,, Salisbaryensis, E. von Hauer 
„ securis, von Dittmar ^ 
„ g aster optychus, von Dittmar 
,, spirolohus, von Dittmar 
,, Goniatites, F. von Hauer 
,, triadicus, E. von Mojsisovics 
^ Proceed. Boston Soc. Nat. Hist. 1883, vol. xxii. p. 270. 
^ Bull. United States Geol. Surv. 1884, vol. i. p. 17, pis. vii., Aiii., ix. 
^ Ann. & Mag. Nat, Hist. 1890, vol. v. pp. 389, 392. 
^ Die Cephalopoden der Mediterranen Triasprovinz, 1882, p. 281. 
° Das Gebirge um Hallstatt, 1873, p. 25, Tat. xi. 
® Haidinger’s Naturwiss. Abhandl. 1849, Band iii. Abth. i. p. 6, Taf. ii. 
ff. 1-3. 
’’’ Ibid. p. 7, Taf. ii. ff. 4^8. 
® Zur Fauna der Hallstadter Kalke, in Geogn.-palaont. Beitriige, 1866, 
Band i. Heft ii. h, p. 351 (33), Taf. xii, ff. 3, 4, 
3 Ibid. p. 350 (32), Taf. xii. ff. 1, 2. 
10 Ibid. p. 352 (34), Taf. xiii. ff. 1, 2. 
11 Haidinger’s Naturwiss. Abhandl. 1849, Band iii. Abth. i. p. 4, Taf. i. 
ff. 9-11. 
1^ Das Gebirge um Hallstatt, in Abhandl. der k.-k. geologisch. Reichsanst. 
1873, p. 27, Taf. xiv. ff'. 1-4. 
