AMMONITID^. 1*1 



ture at the columellar side produced into a lobe, processes 

 wanting at the siphonal side and on the flanks ; lines of growth 

 and sculpture parallel to the margin of the aperture, at the suture 

 bent forwards ; sculpture feeble, mostly consisting of radial lines 

 or interruptions ; sutural line with few lobes, lateral lobes and 

 saddles symmetrically divided, columellar lobe two-pointed. No 

 aptychus. 



The forms of the Trias diverge herefrom in such a wa.j, that 

 in them the lines of growth and sculpture, as in Phylloceras, are 

 directed forward at the siphonal side, and that the structure ot 

 the saddles is monophyllic. 



Lytoceras corresponds to the Fimbriati group of Ammonites. 



MONOPHYLLTTES, Mojs., ISTO. Differs in the saddles being 

 monophyllic. L. sphserophyllmn^ Hauer. 



OPHICERAS, Griesbach, 1881. Compressed ; section of whorls 

 oval and widening near the umbilicus, the latter large and shal- 

 low ; thick, covered with fine wrinkles or growth-lines of sigmoid 

 shape, becoming fine ribs in the body-chamber ; at irregular 

 intervals the shell swells into rounded bumps, largest near the 

 umbilical margin ; the periphery is rounded, and the wrinkles 

 or folds run across it and join with those of the other side. 

 Both in general shape and number and arrangement of the lobe- 

 lines, this subgenus closely resembles the Lytoceratite groups 

 Monophyllites and Phjdloceras, and it may be said to be an 

 earlier stage of those forms. C. Tibeticum, G-riesb. (xl, 45). L. 

 Trias; Himalayas. 



Phylloceras, Siiess, 1865. 



Syn. — Rhacoceras (Agassiz), Hyatt, 1861. 



Distr. — tt sp. Triassic, Jurassic, Cretaceous. P. ocuUum^ 

 Mojs. (xxxix, 38, 39). P. {Rhacoceras) heterophyllum, Sowb. 

 (xxxiv, 51, 52). 



Shell discoidal, involute, with feeble sculpture, sometimes with 

 constrictions or varices, lines of growth directed forwards ; 

 body-chamber short, margin of aperture simple with somewhat 

 produced lobes on the external side ; no aptychus ; lobes numer- 

 ous, diminishing regularly in size, laterals without subdivision 

 into principal paired branches ; leaves or lobes of the saddles 

 very much rounded ; antisiphonal lobe two-pointed. 



This genus is remarkable for its persistence in the secondary 

 strata. The triassic forms are characterized by their less numer- 

 ous lobes, and more open umbilicus. Prof. Meek includes a few 

 American cretaceous species in the genus. 



Harpoceratse. 

 Aperture with more or less developed lateral ear-like prolon- 

 gations ; sutural line with accessory lobes ; surface ornamented 



