78 AMMONITIDZ. 
with straight or curved radiating ribs. Aptychus calcareous, 
grooved, formed of two plates. 
Harpoceras, Waagen, 1869. 
Syn.—Grammoceras, Hyatt, 1867. Leioceras, Hyatt, 1867. 
Lioceras, Bayle, 1878. Hammatoceras, Hyatt, 1867. Ludwigia, 
Bayle, 1878. Phymatoceras, Hyatt, 1867. Pelecoceras, Hyatt, 
1867. Tropidoceras, Hyatt, 1867. Waagenia, Bayle, 1878. 
Sonninia, Bayle, 1878. 
Disir.—96 sp. Jurassic. Harpoceras ( Tropidoceras) Acton, 
d’Orb. (xxxviil, 17,18). H. (Grammoceras) serpentinum, Schl. 
(xxxv, 65, 66). H. (Letoceras) 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. 
Aptychus 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 civided 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. (£cotraustes, Waagen, 1869. 
Distr.—i1 sp. O. subradiata, Sowb. (xl, 57). O. (Neumayria) 
fulgens, Trautsch. ‘xxxix, 88, 89). 
Shell with umbilicus usually narrow, external side either 
rounded only on the body-chamber or on all the whorls. Seulp- 
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 symmetrical branches. 
Aptychus divided, calcareous, thick, folded (Apt. lamellosus) ; 
muscles of attachment near the margin in the lower half of the 
shell. 
Oppelia branches off in the lower Oolite with Opp. subradiata 
from Harpoceras; the last representatives, as far as we know, 
