74 AMMONITID^. 



S. cristata, Deluc. (xxxv, 67). S. (Mortoniceras) vespertinus, 

 Morton == S. Texanus, Roemer (xxxvi, 86). 



This genus embraces the very natural group of Cristati ; to 

 these may be added Schl. Germari, Reuss., whose affinity to 

 these is indicated, besides other striking characters, by a toothed 

 keel. Shell strongly keeled, usually with strong ribs curved 

 forwards on the flanks ; body-chamber two-thirds of a whorl long, 

 drawn out at the sickle-shaped aperture into a long', beak-like 

 process, which is either prolonged in conformity with the curva- 

 ture of the spiral or bent outwards. Siphon very stout, usually 

 lying in the keel, which is often cut off from the lumen of the 

 shell by a calcareous septum. Lobes not much branched, with 

 bodies which are narrower than the saddles ; only one distinct 

 auxiliary lobe ; which is wanting in some forms. Siphonal lobe 

 usually as long or longer than the first lateral. In some species 

 a great reduction in the number of branches of the lobes takes 

 place, so that they approach a Ceratitic form. (Schl. senequeri 

 and halophylla.) 



Placenticeras, Meek, ISTO. 



JDistr. — Cretaceous ; United States, India. A. placenta^ DeKay 

 (xxxvi, 82). 



Shell with the very narrow periphery truncated, and often 

 provided with a row of compressed alternating nodes along each 

 margin; volutions about three-fourths embraced by the next 

 succeeding outer one ; septa with the lateral sinuses provided 

 with more or less branched and digitate terminal divisions ; 

 umbilicus small or moderate. 



sPHENODiscus, Meek, 1872. Shell with periphery cuneate; 

 umbilicus very small ; volutions each almost entirely embraced 

 by the succeeding one ; septa with the first five or six lateral 

 sinuses provided with only a few short, nearly simple, obtuse 

 divisions ; while the others are simple, and usually broadly reni- 

 form at the ends. Cretaceous ; United States, Europe. Amm. 

 lobatus, Tuomey. 



Meek thinks that some of the species of Pinacoceras, Mojsi- 

 sovics, will fall into this group ; and that that genus is too 

 comprehensive. Sphenodiscus equals the Clypeiformi grovip 

 of Ammonites. 



NEOLOBITES, Pischcr, 1882. Shell flattened, sharply carinated; 

 lobes and saddles simple, not truncate, resembling those of the 

 triassic Lobites. P. Vibrayeanus^ d'Orb. Cenomanian. 



BucHiCERAS, Hyatt, \815. 

 Dedicated to Dr. L. von Buch, a German naturalist. 

 Distr. — Cretaceous. B. Syriacum, Buch. 

 Shell ornamented with strong ribs, dichotomous, from tuber- 

 cles near the umbilicus ; ribs interrupted at the periphery ; lobes 



