90 INFERIOR OOLITE AMMONITES. 



Hyperlioceras was undoubtedly descended from Pseudolioceras, and had, therefore, 

 nothing to do with Lioceras beyond being a parallel coeval genus, possessing a 

 similar aspect. The suture-line of Hyperlioceras, with its array of small auxiliary 

 lobes, at once suggests to us the genus Pseudolioceras; and the peculiar carination 

 of the ventral area upon the body-chamber of the young forms of Pseudolioceras 

 (Plate XX, fig. 6) brings the Hyperlioceras-ch&r&cter to our minds. In the shape 

 of Hyperlioceras discoideum we see a distinct reversion to the shape of Pseudo- 

 lioceras compactile, such as the triangular aperture, very sharp external edge, and 

 small ventral area almost occupied by the carina. In the mode of ribbing gene- 

 rally there is no great difference between the two genera ; Hyperlioceras has sub- 

 falciform ribs in youth, which very quickly give place to a smooth test, ornamented 

 with what must be called sigmoidal strias. Why the hollow carina of Pseudo- 

 lioceras should have given place to the very strong solid carina of Hyperlioceras, I 

 cannot say ; and the concave inner margin of the latter genus is another singular 

 fact. If I am correct in deriving Hyperlioceras from Pseudolioceras, it seems very 

 strange that it should possess the concave inner margin like Lioceras, which genus 

 it also approaches in many other respects, while the inner margin of Pseudolioceras 

 is straight, and falls at right angles towards the umbilicus. We see, however, 

 that the inner margin of Lud.wigia is also concave ; and we thus have the extra- 

 ordinary fact that three practically coeval genera, belonging to three different 

 genetic series, have an inner margin of the same peculiar shape. We happen also 

 to find the same concave inner margin in Hildoceras, a genus coeval with Pseudo- 

 lioceras and the earlier forms of Lioceras, but evidently in no way so closely allied 

 to them as those genera are to each other. Consequently, though we recognise 

 the peculiar fact that several different genera of Ammonites, existing more or less 

 together during a limited period, possessed in common a character like this, yet 

 we must come to the conclusion that the presence of a concave inner margin is no 

 indication of intimate consanguinity, and, in these forms, is of no value for the 

 purpose of classification. 



All the species of this genus with which I am acquainted are especially 

 peculiar to the Concavum-heds, and occur chiefly at Bradford Abbas j 1 but, 

 singularly enough, specimens of the same species were obtained by the late Mr. E. 

 Witchell, F.G.S., from the Gryphite-grit of Frith Quarry and Rodborough Hill, 

 near Stroud, Gloucestershire. Not only so, but several other species of Ammonites 

 which are found in, and are essentially peculiar to, the Concavum-heds at Bradford 



1 Mr. E. Wilson, F.G.S., has discovered species of this genus at Dundry in Somerset. With his 

 usual kindness he has submitted them to me for examination. They are very poorly preserved, and are 

 not sufficiently numerous for me to say what their characters may be, except that they belong to the 

 genus Hyperlioceras. They come from a rubbly rock (marl and stone intermixed), associated with 

 Terebratula Eudesi. This rubbly rock is probably the exact horizon of the Bradford- Abbas Concavum- 

 btds, and reminds one very forcibly of similar deposits near Sherborue in Dorset. 



