CLASS V 



CEPHALOPODA 



671 



Subfamily F. Placentice ratin ae Hyatt. 



Coiupressed, involute, higli-whorled forms, witli venters flat coinijressed or concave 

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

 smooth. Septa complex, with 

 irregulär outlines, and narrow 

 saddles. 



This group appears to be little 

 modified from the ancestral Cosmo- 

 ceratinae,! and of all tlie so-called 

 Pseudoceratites of the Cretaceous it 

 is nearest to the typical form. 



FlacenHcerasM.Qek ; JDvplacomo- 

 ceras Hyatt ; Forbesiceras Kossmat. 

 Cretaceous. 



Family 29. 



Bngonoceratidae 

 Hyatt. 



Indoceras ismaeli (Zittel). Upper Seiionian ; Libyan 

 Desert west of Oasis Dachsei. 



Shell compressed, patelliform, 

 narrowly uvihilicate, high lohorled. 

 Venter ßattened or rounded, or 

 acute. Flanks with broad low folds 

 which often end in marginal keels, 

 more seldom in knots or spines. 



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

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

 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 ; Hoplitoides von Koenen ; Indoceras 

 Noetling (Fig. 1309); Sphenodiscus Meek. 

 Cretaceous. 



Family 30. Pulchelliidae Douville. 



Form involute and high whorled. Venter 

 ßattened or rounded or acute. Flanks smooth, 

 or ornamented loith ribs or knots. Septa not 

 digitate, being mostly either ceratitic or gonia- 

 titic in character. Lobes and saddles shcdlow, 

 löith broad saddles and narrow lobes. External 

 saddle divided into several secondary lobes. 

 Auxiliary lobes two to three in number. 



The Pulchelliidae were probably derived 

 from the Hojilitinae. Pulchellia Douville ; 

 Metoicoceras Hyatt ; Knemiceras J. Boehm ; 

 Buchiceras Hyatt ; lloemeroceras Hyatt ; Tissotia 

 Douville (Fig. 1310). Cretaceous. 



Vir.. 1310. 



Tissotia fourndi Bayle. Cenomanian ; Mzabel- 

 M'sai, Algiers (after Bayle). 



^ Smith, J. P., The developmeiit and i)liylogeiiy of Placenticeras. 

 Sei., 3rd ser., Geol., 1900, vol. 1. No. 7. 



Proc. California Acad. 



