252 ORGANIC REMAINS. 



a small specimen of Sowerby's a. concavus, Tab. 94, Fig. 2. It has 

 a faint spiral fuiTOw on one side.^ — -We have another shell with the 

 same kind of strong waved ribs, but having the internal angles of the 

 aperture sharp, as in No. 8. This species, which is also from the 

 alum shale, and which is not figured, may be named a. Soulhiensis. 



No. 6, PI. XII, is of a different character from the five species 

 last described. Its spire is not flat, but rounded, and without a keel, 

 the aperture being nearly circular ; and its ribs, or rather strias ( for 

 they are very small ) are not sigmoidal, but straight. It greatly re- 

 sembles the spiral horns that are used as snuff-boxes ; and as it is 

 generally found in the state of cast, with the beautifully foliated septa 

 displayed, it has a rich appearance, especially when it is pyritous. 

 This species, which is trom the alum shale, we may name a. cornucopia. 



No. 10, PL XII, and Nos. 10, 11, PI. XIII, approach still nearer 

 to the nautilus family, having only a small part of the inner whirls 

 exposed. They differ from the ammonites already described, in 

 having crenulated keels. — No. 10, PI. XII, is found in the oolite and 

 the grey limestone of Malton. It is a lenticular shell, with a sharp 

 crenulated keel, and sagittate aperture; having half the outer whirl 

 marked with large and distant ribs ; and the other half, towards the 

 keel, with numerous curved small ribs. The a. splendens of Sowerby, 

 Tab. 103, is marked like it; but, as it does not fully coincide with it, 

 we may name our shell a. Maltonensis. — Another shell of the same 

 shape, but with slender striae instead of ribs, is also met with in the 

 Malton limestone. It seems to be Sowerby's a. excavatus. Tab. 

 105. This species and the last are nearly of the same size, each 

 measuring four or five inches in diameter. — No. 10, PI. XIII, is a rare 

 and beautiful little flat shell, from the calcareous sandstone of Ro wlston 

 scar. It has on the back a double crenulated or serrated keel, or 

 rather, a double row of minute knobs, with a narrow space between 

 the rows, rather depressed. The knobs are at the ends of its waved 



