MULTILOCULAR SHELLS. 251 



The markings of No. 9, PI. XII, resemble those of a. communis, 

 and still more those of a. giganteus. Like the latter, it is from the 

 oolite, and is of a great size, our specimen being eight inches broad, 

 and two thick ; but it differs from a. giganteus, in having the exterior 

 whirl vastly larger than the next, which it partly conceals, as is the 

 case also in No. 1. This shell we may name a. Piclceringius. 

 Sowerby's a. Nutjieldensis, Tab. 108, resembles it. 



This shell and a. Hildensis make a distant approach to the 

 nautilus family, in having a very large outer whirl, partly concealing 

 the interior whirls. This remark applies much more to the ammonites 

 that remain to be described, which ought perhaps to be arranged 

 under a new genus, distinguished by the appropriate name ammo- 

 nautilus, as suggested by Mr. Parkinson. 



No. 7, PI. XIII, corresponds with the a. elegans of Sowerby, 

 Tab. 94, Fig. 1 ; having the same form, the same sigmoid al ribs, sharp 

 keel, and truncated internal angles. It is not uncommon in the lias 

 nodules. The specimen figured is small, but singular, having 

 portions of the chambers hollow, containing when discovered a 

 considerable quantity of oil. — No. 8, PI. XIII, greatly resembles 

 this last shell, and has the same localities ; but the internal 

 angles of the aperture or spire, instead of being truncate or bevelled, 

 are sharp and rather prominent, the margin of the outer whirl pro- 

 jecting somewhat over the next whirl. There is also a groove, as in 

 a. Hildensis, generally dividing the whirl longitudinally, or rather 

 spirally. This shell is often pyritous, and of great beauty. As it 

 occurs chiefly on the shores of the Mulgrave estates, we may name it a. 

 Mulgravms. — No. 4, PI. XIII, belonging to the same strata, differs 

 from No. 7, chiefly in having the internal angles rounded, giving the 

 aperture an oval form. Hence we may call it a. ovatus. It differs 

 &om the a. ellipticus of Sowerby, Tab. 92, Fig. 4, in having sigmoidal 

 ribs. — No. 5, PI. XIII, also from the aluminous strata, appears to be 



