18 AMMONITID^. 



with straight or curved radiating ribs. Aptychus calcareous, 

 grooved, formed of two plates. 



Harpoceras, Waagen, 1869. 



Syn. — Grrammoceras, Hj'att, 1867. Leioceras, Hyatt, 186*1. 

 Lioceras, Bayle, 1878. Hammatoceras, H3^att, 1867. Ludwigia, 

 Bayle, 1878. Phymatoceras, Hyatt, 1867. Pelecoceras, Hyatt, 

 1867. Tropidoceras, Hyatt, 1867. Waageiiia, Bajde, 1878. 

 Sonninia, Bayle, 1878. 



Distr. — 96 sp. Jurassic. Harpoceras ( Tropidoceras) Actaeon, 

 d'Orb. (xxxviii, 17, 18). H. (Grammoceras) serpentinum^ Schl. 

 (xxxv, 65, 66). H. {Leioceras) complanatum, Brug. (xxxix, 

 36,37\ H. (Hammatoceras) insignis, Schloth. (xxxviii, 15, 16). 



External form of the shell variable, outer side always carinate 

 or angular ; sculpture consisting of more or less distinct sickle- 

 like ribs. Margin of aperture sickle-shaped, or with ears, with 

 pointed external lobes ; body-chamber embracing one-half to 

 two-thirds of a whorl, carinate to the margin of the aperture. 

 Apt3'chus divided, thin, calcareous, with a thick, shelly layer, 

 more or less folded. 



Lobes mostly not deeply notched, always two lateral lobes 

 and almost always auxiliaries. Siphonal lobes ending in two 

 diverging branches, usually shorter than the first lateral ; laterals 

 not divided into symmetrical halves. 



This genus corresponds to Buch's group Ammonites Falciferi. 



HiLDOCERAS, Hyatt, 1867. Carina bordered on either side by a 

 groove. H. bifrons, Brug. (xxxv, 63). 



Oppelia, Waagen, 1869. 



Dedicated to the paleontologist, Oppel. 



Syn. — Neumayria, Bayle, 1878. CEcotraustes, Waagen, 1869. 



Distr. — 71 sp. 0. subradiata,8owh.(:sl,51). 0. {Neumayria) 

 fidgens, Trautsch. f xxxix, 88, 89). 



Shell with iimbilicus usually narrow, external side either 

 rounded only on the body-chamber or on all the whorls. Sculp- 

 ture sickle-shaped, body-chamber frequently geniculate, never 

 carinate or angular, embracing one-half to two-thirds of a whorl ; 

 margin of aperture sickle-shaped or with ears, always with 

 rounded external lobes. Siphon stout with calcareous sheath. 

 Lobes moderately branched, siphonal mostly shorter than the 

 first lateral ; lobular bodies slender with almost parallel edges ; 

 lateral lobes divided into two principal sj'mmetrical branches. 

 Aptychus divided, calcareous, thick, folded {Apt. lamellosvs); 

 muscles of attachment near the margin in the lower half of the 

 shell. 



Oppelia branches off" in the lower Oolite with 0pp. subradiata 

 from Harpoceras; the last representatives, as far as we know, 



