260 Mr. J. Lycett on the Upper Lias of Gloucestershire. 



desire to separate them into the forms named A. communis, 

 A. Hollandrei, and A. Braunianus, — a perplexity which is in no 

 degree lessened by the study of numerous specimens. Further 

 investigations into these forms are desirable. 



A. heterophyllus. Badly preserved examples, and few. 



A. cornucopice (A. fimbriatus, Sow.). A single fine example 

 in one of the higher beds. Some casts of young forms, appa- 

 rently of this species, have been procured in the lower zone of 

 the Cynocephala- stage at Nailsworth. 



A. Jurensis. Fragments only in the higher beds. 



A. crassus (A. Raquinianus, D'Orb.). Evidently the same 

 shell as in the lower zone of the Cynocephala-stage at Nails- 

 worth and in the Upper Lias of Yorkshire. 



Ammonites Ilminstrensis, n. sp. 



In its general figure it is scarcely to be distinguished from 

 Ammonites Humphriesianus ; the style of its ornamentation is 

 also very similar to that of the latter species; there are, how- 

 ever, some well-marked differences. In A. Humphriesianus the 

 lateral costse form, with the dorsal, a curvature more or less 

 marked ; in the Lias shell, the ribs pass from the suture straight 

 over the sides and back. Usually two, but sometimes three, 

 dorsal ribs unite with one lateral rib. In A. Humphriesianus the 

 number of dorsal ribs is somewhat greater; but the most con- 

 spicuous distinction consists in the form of the dorsal ribs, which 

 in the Lias shell are much more narrow, elevated, and acute, so 

 that there is a wide space left between each rib. In the young 

 shell the lateral ribs are likewise much elevated and acute, so 

 that they are little larger than the dorsal ribs ; there is also 

 some little distinction in the figure of the volutions, and conse- 

 quently of the aperture, the portion near to the suture over- 

 hanging the preceding volution more than in the Inferior Oolite 

 shell. 



The septa consist of three large principal lobes, much pro- 

 duced, and of two small accessory lobes. The dorsal lobe is 

 much lengthened, with a single, terminal, very elongated and 

 pointed digitation upon each side of the mesial line; there are 

 two smaller lateral digitations ; all the digitations are indented. 

 The superior lateral lobe has its termination trifurcate, the me- 

 sial digitation being pointed, and of immense length ; but the lobe 

 altogether is less lengthened than the dorsal lobe. The inferior 

 lateral lobe is similar in figure to the superior lobe, but is much 

 smaller and shorter. The two accessory lobes are very small and 

 simple, the second being nearly concealed by the convexity near 

 to the suture. The dorsal saddle is of great width, consisting 

 of two principal divisions, of which the outer is much the larger; 



