CLASS V 



CEPHALOPODA 



671 



Subfamily ¥. Placenticeratinae Hyatt. 



Compressed, involute, liigli-wliorled forms, with venters flat compressed or concave 

 in youth, becoming somewhat rounded with age. Surface either tuberculate or 



Septa complex, with 

 outlines, and narrow- 



smooth. 



irregular 



saddles. 



This group appears to be little 

 modified from the ancestral Cosmo- 

 ceratinae,! and of all the so-called 

 Pseudoceratttes of the Cretaceous it 

 is nearest to the typical form. 



Placenticeras Meek ; Dvplacomo- 

 ceras Hyatt ; Forbesiceras Kossmat. 

 Cretaceous. 



Family 29. 



Engonoceratidae 

 Hyatt. 



Fi.;. 1300. 



hidoceras ismaiili (Zittel). Upper Senonian ; Libyan 

 Desert west of Oasis Dachsel. 



Shell compressed, imtdliform, 

 narro%vly wmhilicate, high whorled. 

 Venter flattened or rounded, or 

 acute. Flanks with broad low folds 

 which often end in marginal keels, 

 more seldom in knots pr spines. 



Septa not deeply digitate, lobes xLsually only moderately serrated, saddles often rounded 

 and entire. The external saddle is often divided into several secondary lobes. Tliere 

 are several auxiliary lobes in most genera. 



The Engonoceratidae were probably, derived from the Placenticeratinae, and 



through them from the Cosmoceratinae. 



Engonoceras Neumayr ; Metengonoceras 



Hyatt ; Hoplifoides von Koenen ; Tndoceras 



Noetling (Fig. 1309) ; Sj^henodiscus Meek. 



^^ .. issx Cretaceous. 



Ax 



' '^""' Family 30. Pulchelliidae Douville. 



Form involute and high iohorled. Venter 

 flattened or rounded or acute. Flanks smooth, 

 or ornamented with ribs or knots. Septa not 

 digitate, being mostly either ceratitic or gonia- 

 titic in character. Lobes and saddles shallmo, 

 with broad saddles and narroio lobes. External 

 saddle divided into several secondary lobes. 

 Auxiliary lobes txvo to three in number. 



The Pulchelliidae were j)robably derived 

 from the Hoplitinae. Pulchellia Douville ; 

 Metpicoceras Hyatt ; Knemiceras J. Boehm ; 

 i>«c/w"ce?'rts Hyatt; /t'oewCT'ocer-as Hyatt ; Tissotia 

 Douville (Fig. 1310). Cretaceous. 



Fui. 1310. 



Tissotia fourneli Bayle. Cenomanian 

 M'sai, Algiers (after Bayle). 



Mzabel- 



^ Smith, J. P., The development .iiirl phylogeny of Placeuticeras. 

 Sci., Srd ser.. Geol., 1900, vol. i. No. 7. 



Proc. California Acad. 



