SIXTH, OR OXYNOTICERAN BRANCH. 217 



layer, which formed the partition above the keel, and above this again a succes- 

 sion of finer layers ; but these did not fill up the interior of the keel completely. 

 A hollow portion or zone filled in the fossil with pyrites, occupied the outer 

 half of the interior of the keel. My notes and sketches make no mention of any 

 dark layer in these specimens. 



Oxynoticeras Simpsoni, Hyatt. 



Summ. PI. XIII. Fig. 11. 



Amm. Simpsoni, Simps., Amm. York. Lias, p. 37. 

 Amaltheus Simpsoni, Wright, Lias Amm., p. 392, pi. xlvii. fig. 4-7. 



Amm. oxynotus (pars), Dum., Etud. Pal. Bassin du Rhone, pi. xxxiii. fig. 1, 4 ? (not fig. 2, 3, 5). 

 Locality. — Whitby. 



This species is quite different in form, sutures, and the amount of involution, 

 and it is better to hold it as distinct than to confuse it with oxynotum. 



It is admirably figured by Wright. The shell is considerably more tumid, the 

 whorl thicker and stouter than in oxynotum, and this peculiarity is observable even 

 in the young. The amount of involution is greater, and consequently the um- 

 bilicus is smaller, than in that species. The margins of the sutures are much 

 simpler, especially as regards the auxiliary lobes and saddles than in oxynotum. 

 It is intermediate in all its characteristics between oxynotum and Lymense, and this 

 is an additional reason for separating it from the former. 



If we are right, either this species or a form transitional to it is found in the 

 basin of the Rhone. 



Oxynoticeras Lymense, Hyatt. 



Summ. PI. XIII. Fig. 13. 



Amaltheus Lymensis, Wright, Lias Amm., pi. xlvi. fig. 1-3; pi. xlvii. fig. 1-3; pi. xlviii. fig. 1, 2. 



Amm. Smmanni, Dum., Etud. Pal. Bassin du Rhone, p. 154, pi. xl., xliii. 



Amm. oxynotus, Hauer, Ceph. Nordbstl. Alpen, pi. xiii. fig. 3, 4, 8, 9 (not fig. 6, 7). 



Locality. — Lyme Regis. 



This. is merely a more involute form of Oxyn. oxynotum, which deserves a sep- 

 arate name on this account, but is closely related to that species. 



Oxynoticeras numismale, Hyatt. 



Amm. oxynotus numismalis, Quenst., Amm. Schwab. Jura, p. 289, pi. xxxvii. fig. 1-3, 6, 7 (not fig. 4, 5). 

 Amaltheus Wiltshirei, Wright, Lias Amm., pi. xlviii. fig. 3. 



Locality. — Boll. 



This species has, according to Quenstedt's figures, young similar to the adults 

 of oxynotum, and the adult has a hollow keel. This is lost in. old age, the whorl 

 becoming rounded as in Lotharingum. It seems to be an extremely geratoloo-ous 

 form of the first subseries surviving in the Middle Lias. The sutures are oxynoti- 

 ceran in outline, and confirm this view of the affinities of the species. 



Quenstedt considers it identical with Oxyn. Oppeli, which is, however, a stouter 

 form at the same stages of growth. He also erroneously identifies it with Oxyn. 



28 



