652 



MOLLUSCA 



PHYLUM VI 



but retaining the phylloid ending, and witli the marginal saddles retaining the 

 monophyllic outlines. Antisiplional lobe with entire sides, or with only one pair of 

 lateral branclies, and extremities bifid. 



Rhacophyllites Zittel (Fig. 1247); EitphylUtes Wähner ; Phylloceras Suess (Figs. 



ifi a5 «•* a3 a2 ai l 



Fio, 1250. 



Suture-line of Phylloceras nüssoni (Heb.), 

 Upper Lias. 

 SL, Ventral or slphonal lobe ; L, First, and l, Second lateral lobes 



Fig. 1251. 



l Li AL 



Sutiire-line of Sowerhiceras tortisulcatum (d'Orb.) 

 (after Quenstedt). 



^ ^ ai - 6, Inner or .so-called auxiliary lobes ; 



ri^Line of'involution ; Li,' Second dorsal lobe ; AL, Antisiphonal lobe. 



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

 D. (Phylloceras) rakosense (Herbicb). Schistophylloceras Hyatt. Type S. (Phylloceras) 

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

 Trarjophylloceras Hyatt. Type T. (Phylloceras) heterophyllus-numismalis (Qiienst.). 

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



Family 20. Lytoceratidae Neumayr. 



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

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

 rounded, whorls little emhracing. Surface often ornamented ivith simple rihs or rows 

 of knots. Septa deeply divided, with usually tvjo lateral lohes and an auxiliary. The 

 first and often the second lateral lohes and saddles are deeply hifid. 



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

 Scaphites and other degenerate groups Coming from different Stocks. The Lytoceratinae, 

 however, appear to be monophyletic, and to liave been derived from Monophyllites. 



Subfamily A. Lytoceratinae Mojsisovics (pars). 



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

 often crenulated, transverse bands of growth. Antisiphonal 

 lobe with two long internal branches bending inwards and 

 attached to surfaces of the septa. Siphonal lobe 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 fuU-grown shells. 



Lytoceras Suess (Thysanoceras Hyatt) (Figs. 1252, 

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

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

 Lytocera.^fimbriaium{Sovfh.). Hyatt. Type P. (Amm.) hircinum (Schloth.). Jura. 



Middle Lias ; Würtemberg. m, u xr j. n i ^ 



Cross-section (cf. Fig. 1148). ^ eiragonites Kossmat ; Gaudryceras Grossouvre. Cretaceous. 



Subfamily B. Macro8Caphitinae Hyatt. 

 Symmetrical, closely coiled, discoidal ammoniticones during \oimg stages (and 

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



