16 AMMONITIDJB. 



LiLLiA, Bayle, 1818. In the yoimg shell the ribs are simple or 

 bifurcated, commencing with tubercles at the umbilical region ; 

 later the ribs are simple and the shell resembles Agassiziceras. 

 Perhaps this group would be better placed near Harpoceras : 

 the limit between the latter genus and Ammonites is very diffi- 

 cult to trace, without the aid of the apt3'^chus. 

 iEaocERAS, Waagen, 1869. 



Syn. — Mycroceras, Hyatt, 1861. Androgynoceras, Hyatt, 

 1861. Liparoceras, Hyatt, 1861. Deroceras, Hyatt, 1861. Per- 

 onoceras, Hyatt, 1861. Platypleuroceras, Hyatt, 1861. Cyclo- 

 ceras, Hyatt, 1861. Psiloceras, Hyatt, 1861. 



. Distr. — 4 Cretaceous, 54 Liassic species, ^goceras {Micro- 

 ceras) biferum^ Quenst. (xxxvii, 96, 91). J5J. (Androgynoceras) 

 hybridum^ Hyatt (xxxvi, 83, 84). ^. (Lyparoceras) Henleyi^ 

 Sowb. (xxxvi, 85). JS. (Deroceras) Ziphius, Ziet. (xxxvii, 95). 

 /^. (Feronoceras) muticum, d'Orb. (xxxviii, 13, 14). JE. (Platy- 

 pleuroceras) latecostatum, Sowb. (xxxviii, 19). ^. (Cycloceras) 

 Valdani, d'Orb. (xxxix, 34, 35). ^. (Psiloceras) psilonotum, 

 Quenst. (xxxvii, 2, 3;. 



Shell mostly compressed, composed of many whorls, embra- 

 cing but little, sometimes provided with nodose or externally 

 bifurcate ribs ; never with true sickle-like ribs ; not carinate ; 

 body-chamber usually a whorl long, in the geologically younger 

 forms somewhat shorter. Aperture simple without lateral ap- 

 pendages, with very weak external lobes and a constriction ; a 

 single corneous aptychus. Lobular line strongly notched, upper 

 lateral longer than the siphonal, lower lateral not always present ; 

 usually with a depending siphonal lobe. Lobular bodies narrow, 

 not wedge-shaped ; antisiphonal two-pointed. 



The true ^goceras died out in the middle Lias. 



iEgoceras corresponds to the group Ammonites Capricorni ot 

 Bueh. 



SCHLOTHEIMIA, Bayle, 1818. Ribs meeting exteriorly, where 

 they form an angle directed towards the aperture. ^. angu- 

 latum, Schloth. 



Lytocerse. 



Body-chamber short, two-thirds of the last whorl ; aperture 

 simple. IS"© aptychus. 



Lytoceras, Suess, 1865. 



Syn. — Thysanoceras, Hyatt, 1861. 



Distr. — 62 species from the Trias, Jura and Cretaceous. L. 

 Henleyi, Sowb. (xxxvi, 85). L. Moreleti, Hauer (xxxviii, 28, 29). 

 L. (Thysanoceras) fimbriatus, Sowb. (xxxiii, 45, 46). 



Shell flattened, discoidal, whorls but little involute or simply 

 in contact ; bodj^-chamber two-thirds of a whorl, margin of aper- 



.,Jt 



