194 
TIL Family Lytocsratipa, Newmayr. 
This family includes several groups which differ from each 
other much as regards their external form, but which neverthe- 
less appear to have close genetic relations in their internal 
structure. They are characterised by having a short body- 
chamber, about two thirds of a whorl in length, a simple mouth- 
border slightly produced on the columellar side; but in all the 
other features there is a wide difference of structure. 
This family includes the typical groups Lytoceras and Phyl- 
loceras, and others which differ much from them in external 
form, as Hamites, Turrilites, and Baculites. 
The Aptychus appears to be absent in this family; at least, 
at present it has not been found. 
Genus Lyrocrras, Suess.—Shell discoidal, more or less flat; 
umbilicus large and open; involution slight, whorls round, only 
slightly embracing each other around the spire. Body-chamber 
two thirds of a whorl in length; mouth-border simple, with 
intermittent contractions, and prominent fimbrie; columellar 
side with a lappet, which rests on the preceding whorl; the 
yentral and lateral sides without any prolongation. The 
sculpture and lines of growth parallel with the mouth-border ; 
near the spiral suture they bend a little forward. Sculpture 
feeble, consisting mostly of small radial lines, and intermittent 
contractions of the shell, with corresponding fimbriz or promi- 
nent fringed ribs at certain intervals of growth (fig. 43). 
Suture line very complicated. Lobes 
few, much branched; lateral lobes and 
saddles divided into small uniform sym- 
metrical digitations; only two lateral 
lobes; anda large columellar lobe covered 
by the former whorl. No Aptychus has. 
as yet been found. 
This genus commences in the Trias. 
Lyt. Morloti, Hav.; Lyt. spherophyllum, 
Hav.; Lyt. patens, Moss. 
It is represented in the Lias formation 
Fic,43.—Lytoceras fimbriatum, 
Sow. 
