652 



MOLLUSCA 



PHYLUM VI 



but retaining the pliylloid ending, and with the marginal saddles retaining the 

 monoijhyllic outlines. Antisiphonal lobe with entire sides, or with only one pair of 

 lateral branches, and extremities bifid. 



Rhacophyllites Zittel (Fig. 1247); Euphyllites Wiihner ; Phylloceras Suess (Figs. 



a6 a^ a-i a3 



Fig. 1251. 



I Li AL 



Suture-line of Sovcrbiceras fortisulcatum (d'Ovb.) 

 (after Queustedt). 



Suture-line of Phj/lloccras nihsoni (Heb.). 

 Upper Lias. 



SL, Ventral or siphonal lobe ; /., First, and /, Second lateral lobes ; ai -8, Inner or so-called auxiliary lobes ; 

 n, Line of involution ; Li, Second dorsal lobe ; AL, Antisiphonal lobe. 



1140, 1248-1250) ; Soicerbiceras Paroni and Bon. (Fig. 1251) ; Basijceras Hyatt. Type 

 D. (Phylloceras) rakosense (Herbich). Schistoplmjlloceras Hyatt. Type 8. {Phylloceras) 

 aulonotum (Herbich). Geyeroceras Hyatt. Type G. {Phyll.) cylindricum (Geyer). 

 Tragophylloceras Hyatt. Type T. (Phylloceras) heterophyllus-numismalis (Quenst.). 

 Menecjhiniceras Hyatt. Type M. (Phylloceras) lariense (Menegh.). Trias to Cretaceous. 



Family 20. Lytoceratidae Neumayr. 



Shell widely umhilicate, sometimes forming a loose or snail-like spiral, sometimes 

 even hook-shaped. Body chamber two-thirds to three-fourths of the last volution. Aperture 

 rounded, irhorls little embracing. Surface often ornamented with simple ribs or rows 

 of knots. Septa deeply divided., with usually turn latercd lobes and an auxiliary. Tlie 

 first and often the second lateral lobes and saddles are deeply bifid. 



In all probability the family Lytoceratidae is not monophyletic, some of the 

 Scapthites and other degenerate groups coming from different stocks. The Lytoceratinae, 

 however, ajipear to be monophyletic, and to have been derived from Monophyllitcs. 



Subfamily A. Lytoceratinae Mojsisovics (pars). 



Includes only closely coiled, discoidal and involute shells with somewhat prominent, 



often crenulated, transverse bands of growth. Antisiphonal 

 lolje with two long internal bi^anches bending inwards and 

 attached to surfaces of the septa. Sij^honal lolie short 

 like that of Phylloceras, and siphonal saddles narrow. The 

 first lateral saddles small and short, the first lateral lobes 

 much longer than the ventral.- Eeduction of lobes along 

 the line of involution is such that there are commonly 

 only six to eight in full-grown shells. 



Lytoceras Suess (Thysanoceras Hyatt) (Figs. 1252, 

 1253). Jura and Cretaceous. Alocolytoceras Hyatt (Fig. 

 1254). Type A. (Amm.) germainei (d'Orb.). Pleurolytoceras 

 T.!itiM-riwjimhriatnm(Sov!h.). Hyatt. Type P. (Amm.) Mrcinum (Schloth.). Jura. 

 Cross-secti'on^cf^^'' ms^^^^^^ TchYtr/o « ?'<es Kossmat ; Gaudryceras Grossouvre. Cretaceous. 



Subfamily B. Macroscaphitinae Hyatt. 



Symnu^trical, closely coiled, discoidal ammoniticones during young stages (and 

 persistently so in primitive forms), but becoming uncoiled in gerontic stages or earlier 



