144 



INFERIOR OOLITE AMMONITES. 



convergence towards some of the narrow-umbilicate species of that genus, yet its 

 suture-line is more developed — the ornamentation being more florid ; and its ribs 

 do not show the strong sweep on the ventral area which is characteristic of 

 Grammoceras. Haug 1 placed Am. occidentalis in "the group of Am. Kurrianus" 

 with Am. fallaciosus (Grammoceras, pars); but the above remarks will apply to 

 this determination also. 



The lobe-line of this genus agrees with the lobe-line of the family Hildo- 

 ceratidse generally (see Plate A). The superior and inferior lateral lobes are as 

 much, or more, developed than in the most developed genera, namely Lioceras, 

 Pseudolioceras, and Hyperlioceras ; but the auxiliary lobes, in consequence of the 

 involute shape being only a lately-acquired character, are much less developed. 

 The lobe-line resembles that of Harpoceras most closely, but may be distinguished 

 by the much smaller accessory lobe in the siphonal saddle, the broader superior- 

 lateral lobe with much more prominent trifurcation, and the different disposition 

 of the auxiliary lobes. (The strong, distinctive, falciform character of the ribs 

 in Harpoceras, especially the sweeping curve on the outer lateral and ventral 

 areas, is absent altogether from Haugia.) The lobe-line also resembles that of 

 Grammoceras, to which I have already alluded. 



A consideration of the above remarks will show that there is every reason to 

 regard the inclusion of Haugia in the family Hildoceratidse as correct. At the same 

 time the very divergent opinions which different authors have held, concerning the 

 proper position of various members of this genus, show in how many different genera 

 the species may be placed, if only one character at a time be taken account of. 



The points of resemblance and difference between this and other genera may 

 be shown in a Table thus : 



Features. 



Genera with similar features. 



Differences which these genera 

 present. 



Knobs and ribs. 



Hammatoceras. 



Lobe-line. 



Do. 



Sonninia. 



Do. 



Do. 



Lillia. 



Lobe-line ; solid carina and 

 furrowed ventral area. 



Without knobs ; involute. 



Pseudolioceras. 



Lobe-line ; sigmoidal ribbing. 



Without knobs ; evolute. 



Grammoceras. 



Lobe-line ; subarcuate ribbing 

 with long ventral sweep. 



Lobe-line. 



Harpoceras. 



Falciform ribbing. 



It is noticeable that, notwithstanding the similiarity of lobe-line, no author has 

 put any species of Haugia in Harpoceras, that is, in the Harpoceras falciferum- 

 group, the difference in ribbing being such a striking feature. 



It is very singular that two other species with very similar ornamentation, but 



1 Op. cit., p. 617. 



