HYPERLIOCERAS. 89 



upper edge sometimes overhanging the lower. The inclusion is usually considerable. 

 The adult shells have a sigmoidal shaped mouth-border ; but the young possess a 

 short, pointed process on the lateral area. In the sutures (Plate A, figs. 23, 24, 25), 

 the siphonal lobe has two short terminal branches ; the siphonal saddle has an 

 accessory lobe dividing it into two rather unequal portions, and is somewhat 

 trenched upon by the digitations of the lobes ; the superior lateral lobe is not 

 much longer than the siphonal, and is sometimes scarcely trifurcate ; the accessory 

 lobe in the superior lateral saddle is feebly developed ; the inferior lateral lobe is 

 about half the size of the superior lateral ; the first auxiliary lobe is well deve- 

 loped. There are about five more auxiliary lobes (besides denticulations), but some- 

 times two may coalesce to form a rather larger one, and thus make three small 

 and one large lobe besides the first one (Plate A, fig. 26). Generally speaking, 

 the succeeding superior lateral lobe just penetrates the preceding, but the septa 

 are rather farther apart from each other than those in Lioceras, though closor 

 than those in Ludwigia* 



Remarks. — The possession of a very strong carina on a peculiarly flattened 

 ventral area, the longer series of auxiliary lobes, and the less developed accessory 

 lobes in the siphonal and superior lateral saddles separate this genus from Lioceras. 

 The carina being solid instead of hollow, the inner margin being concave instead 

 of straight, and the test very soon becoming smooth, separate the genus from 

 Pseudolioceras. 



This genus is the direct descendant from Pseudolioceras, and I believe may 

 have sprung from Ps. compactile. We have seen, however, that the genus Pseudo- 

 lioceras appears to end in the Opalinum-zone, and I have found no species of 

 Hyperlioceras earlier than the Concavum-be&s. Therefore a gap, consisting of 

 the period known as the Murchisonce-zone, has to be filled up ; though I may 

 observe that Moesch 1 quotes his specimens of Hyperlioceras Desori from that 

 zone. Since I incline to the opinion that Hyperlioceras is probably descended 

 more directly from Pseudolioceras compactile than from any other later species, we 

 ought to meet with some connecting forms in the Opalinum-zone. At any rate we 

 have an interesting Ammonite-form traceable, with but a small break, from the 

 Upper Lias to the Concavum-beds of the Inferior Oolite, and undergoing a very 

 distinct change during that period. 



Allusion has previously (p. 21 ) been made to the forms which I place in this genus. 

 Then I regarded them as a division (a strongly carinate group) of the genus Lioceras, 

 especially observing the close similarity which they bore to Lioceras decipiens, inter- 

 medium, &c, and I supposed them to be a mutation of some smooth forms of that 

 genus which we did not know. There were not then in my possession any specimens 

 of the genus Pseudolioceras ; but, having obtained some, I came to the conclusion that 

 1 " Der Aargauer Jura.," ' Beitr. geol. Karte Schweiz,' p. 295. 



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