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 P/u/lloceras, and others which 

 differ much from them in external form, as Hamites, Turrilites, and Baculites. 



The AptycJms appears to be absent in this family ; at least, it has not as yet been 

 found. 



Genus Lttoceras, 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 inter- 

 mittent contractions and prominent fimbriae ; 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 Unes, 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 Apfychus 

 has as yet been found. 



This genus commences in the Trias. Li/t. Morloli, Hauer ; 

 Lyt. sj)hcerophi/Ilum, Hauer; Lyt. patens, Mojs. 



It is represented in the Lias formation by Lytoceras Jimbria- 

 lum. Sow. (fig. 141). By Lyt, Cornucopice, Young ; Lyt. Jurense, 

 Zitt. ; Lyt. Jiircinum, Schloth. ; and Lyt. torulosum, Schiibl. ; 

 Lyt. Eudesianum, d'Orb., in the Inferior Oolite, ^y Lyt. Adelce, Lytoceras fimhriaium,%ov. 

 d'Orb., in the Kelloway. In the Cretaceous rocks by Lyt. Buvalianum, d'Orb. ; Lyt. 

 Honor atianum, d'Orb. ; Lyt. sub-Jimbriatum, 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 llf inches in diameter, with thirty fimbriae on its last whorl. 



Genus Hamites, Parkinson. — With reference 1o the Cretaceous forms having 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, Baculina, Llamulina, Helicoceras, Ptychoceras, and Toxoceras, where the 



'Palseontologia ludica, Jurassic Fauna of Kutcli.' pi. viii, p. 36, 1875. 



