98 INFERIOR OOLITE AMMONITES. 



covered, but this, owing to the overhanging of the margins, can scarcely be seen 

 from outside. 



This species bears considerable resemblance to Hyperlioceras discites, "Waagen, 

 but is at once separable by its very small, peculiarly-constructed umbilicus 

 (occupying only jf^ of the diameter), and by the overhanging inner margin. It 

 is also somewhat thicker, and its sides less parallel. 



Dr. Haug says of this species 1 : — " In der hiesigen Universitats-Sammlung 

 liegen zwei Exemplare aus Sud-England, welche ganz mit Moesch's Abbildung 

 iibereinstimmen. In der Jugend ist die Art glatt und kann daher nicht mit 

 Harp, discites, Waag., vereignt werden. Da Am. Desori, Pictet, einer anderen 

 Gattung angehort, so liegt kein Grand vor den Moesch'schen Namen zu andern." 



Where the test is absent my specimen shows a few obscure ribs, which 

 do not seem to be visible on the test itself of the other side ; but I cannot say 

 anything about its appearance in youth. Among the varieties of Hyperlioceras 

 discites 1 have placed a very smooth form. I therefore doubt if any distinction 

 can be made on the score of smoothness ; but I think that the very small 

 umbilicus, the differently-shaped, thicker whorls, and the overhanging inner 

 margin, are sufficient to separate the two species. Dr. Waagen 2 quotes Ammonites 

 Desori, Moesch (non Pictet) as a synonym of his Ammonites discites, but, as his 

 figure of the latter represents (in my opinion) a sufficiently distinct species, I 

 have followed Dr. Haug in giving effect to Moesch's name. 



This species is extremely scarce, in fact, I only know of the one example 

 which I have figured. It is, in all probability, from the Concavum-beds of 

 Bradford Abbas. Moesch quotes his example from the " MurchisonseSchichten 

 vom Frickberg bei Frick in Aargau." 



Plate XVII, figs. 6 and 7, shows the only specimen of the species which I 

 have seen. It can here be easily compared with forms of Hyperlioc. discites. 



Htperlioceeas discoideum (Quenstedt). Plate XIX, figs. 1 — 4; Plate A, fig. 25. 



1886. Ammonites discoideus, Quenstedt. Am. Schwabischen Jura, pi. lviii, fig. 



1 only. 



a. Discoidal, somewhat compressed, strongly carinate ; whorls sloping con- 

 tinuously from the inner margin towards the ventral area, ornamented merely 

 with very fine sigmoidal lines of growth. Ventral area narrow, flat, carrying a 



1 Loc. cit., p. 624. 



2 Zone des Am. Sowerlyi ; ' Geogn. Pal. BeitrJige,' p. 599 (93). 



