MODERN CLASSIFICATION. 
243 
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 Pkylloceras, and others which 
differ much from them in external form, as Hamites, Turrilites, and Buculites. 
The AptycJbus appears to be absent in this family ; at least, it has not as yet been 
found. 
Genus Lytoceras, Suess. — Shell discoidal, more or less fiat ; 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 inter- 
mittent contractions and prominent fimbrige ; columellar side with a lappet which 
rests on the preceding whorl ; the ventral 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 fimbriae or prominent fringed 
ribs at certain intervals of growth (fig. 141). Suture line very complicated. Lobes few, 
much branched ; lateral lobes and saddles divided into small 
uniform symmetrical digitations ; only two lateral lobes ; and a 
large columellar lobe covered by the former whorl. No Aptychus 
has as yet been found. 
This genus commences in the Trias. Lyt. Morloti, Hauer ; k.-:^'^ / % 
Lyt. sphcerophyllum, Hauer; Lyt. patens, Mojs. 
It is represented in the Lias formation by Lytoceras fimbria- 
tum. Sow. (fig. 141). By Lyt. Cornucopia, Young ; Lyt. Jurense, i-J^ 
Zitt. ; Lyt. hircinum, Schloth.; and Lyt. torulosum, Schiibl. ; Fig i4i 
Lyt. Eudesianum, d'Orb., in the Inferior Oolite. By Lyt. Adelce, Lytoceras fimhriatum,%ow. 
d'Orb., in the Kelloway. In the Cretaceous rocks by Lyt. Duvalianuvi, d'Orb. ; Lyt. 
Llonoratianum, d'Orb. ; Lyt. suh-fimbriatum, d'Orb. 
Dr. Waagen^ has figured and described Lytoceras rex., Waag., from the middle 
Oolite of Kutch, Western India, which is nearly allied to Lytoceras Eudesianum, d'Orb. ; it 
is a magnificent specimen 11 1 inches in diameter, with thirty fimbriae on its last whorl. 
Genus Hamites, ParMnson. — With reference to the Cretaceous forms havmg a conical 
shell bent in one plane or more without the bends being in contact, Professor Neumayr 
remarks that a spiral curve of a particular curvature does not give sufficient data for 
the establishment of a distinct genus. With this view the recognised genera Anisoceras, 
Ancyloceras, BacuHna, ILamulina, Llelicoceras, Ptychoceras, and Toxoceras, where the 
' Pdlceoiitologia Iiidica, Jurassic Fauna of Kutch.' pi. viii, p. 3G, 1875. 
