FOTJETH, OE COEONICERAN BEANCH. 169 



Arnioceras ceras, L. Agassiz. 



Plate II. Fig. 30, 80 a. 



Arnioceras ceras, L. Agassiz, Bull. Mus. Comp. Zobl., I., No. 5, p. 74. 

 Amm. ceralitoides, Quenst., Amm. Schwab. Jura, pi. xiii. fig. 10 (not fig. 8, 9, 11). 

 Amm. Turneri, Quenst., Ibid., pi. xix. fig. 6-8 (not fig. 5-9). 

 Amm. ceras, Hauer, Ceph. Lias Nordbstl. Alpen, p. 25, pi. vi. fio-. 4-6. 

 Localities. — Semur, Whitby, Lyme Regis. 



This species approximates to the aspect of Coroniceras, and also imitates 

 closely the general form and characteristics of some varieties of Ast. Turned. 

 Both in England and Germany, when the interior of the umbilicus or the smooth 

 compressed younger whorls are not preserved, even the most acute observers are 

 apt to consider the adult whorl as belonging to Turned. Some of Quenstedt's 

 figures, especially Fig. 8, Plate XIII., may be either ceras or some allied species 

 of Arnioceras. The keel is prominent, the channels are broader and deeper than 

 usual, the geniculas are prominent and slightly bent forward, the sides, however, 

 flat and slightly convergent, and the pilse straight and smooth, as usual in this 

 genus. The pike begin upon the third quarter of the fourth whorl. 



The superior lateral lobes are somewhat longer than the abdominal lobe. The 

 inferior lateral saddles are one fourth deeper than the superior laterals, the infe- 

 rior lateral lobes one half shorter than the superior laterals on the latter half of 

 the sixth volution. 



A specimen in the Museum of Stuttgardt, locality uncertain, is referred to the 

 Geometricus zone. Two young specimens from the Bucklandi zone, labelled 

 Bucklandi (No. 2756), in Quenstedt's collection, also probably belong to this 

 species. The young are smooth, and the form differs from that of typical 

 ceras only in being a trifle stouter. The channels, perhaps, also appear at quite 

 an early period, but this sometimes occurs in specimens of the typical form. 

 There is also a large specimen from Jettenburg. 



What appeared to be very close allies of this species were collected by Pro- 

 fessor Orton at Ipishguanuna, in Northern Peru. 1 



Arnioceras Bodleyi, Hyatt. 



Plate II. Fig. 23-34 a. Summ. PI. XII. Fig. 7. 



Amm. Bodleyi, Bruck., Murch. Geol. Cheltenh., pi. ii. fig. 7. 



Amm. ceralitoides, Quenst., Die Ceph., pi. xix. fig. 13 ; Amm. Schwab. Jura, pi. xiii. fig. 8, 9, 11. 



Amm. geometricus, Oppel (pais), Der Jura, Wiirt. Jahreshf., XII. p. 199. 



Ariet. semicostatum, Wright, Lias Amm., pi. i. fig. 4, 5, 8 (not fig. 7). 



Am.falcaries, Hyatt, Bull. Mus. Comp. Zobl., I., No. 5, p. 74. 



Ariet. difformis, Blake, Yorkshire Lias, p. 289, pi. vi. fig. 3 a, b. 



Localities. — Whitby, Bonnert, Semur, Raidwangen, Basle, Salins. 



There are three varieties in this species ; one, variety A, figured on Plate II. 

 Fig. 23, has stout, thick whorls ; the second, variety B, has flattened whorls ; and 

 the third, variety C, figured on Plate II. Fig. 24, has flattened whorls like those 

 of the second variety, but they are somewhat wider on the sides. 



1 Proc. Bost Soc. Nat. Hist., 1875, XVII. p 366. 

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