iv YORKSHIRE TYPE AMMONITES Mar. 



Genus, OISTOCERAS, nov. 

 Type, A. fi-guUnus, Simpson, No. 26 



A Capricorn series which develops forward pointing (arrow Hke) 

 j)eripheral costae (oiaros, an arrow). A bituberculate stage developing 

 thickened whorls is produced ; but no sphaerocones are known. 



These four genera, with others, belong to Hyatt's family Liparocera- 

 tida, distinguished from Deroceratidse by simpler suture line without 

 recurved inner lobes. 



Genus, DEROCERAS, Hyatt, 1867 



1867, Foss. Ceph. ; Bull. Mus. Comp. Zool., V, 81, 84, 85, 94. 



The species included by Hyatt belong to three groups — planicosta 

 [A. ziphus), armatus, subarmatus. 



S. BucKMAN (Q.J. Geol. Soc. LIV, 1898, 460) put A. armatus for type 

 of Deroceras, and separated the planicosta series as lacking a name : 

 A. subarmatus is a Dactyloid. 



Result 



Genus, Deroceras, Hyatt, 1867. Genolectotype, A. armatus, 

 J. Sower by. 



Genus, XIPHEROCERAS, nov. 



Type, Mgoceras planicosta ; Wright, 1880. xxv =A. ziphus, Zieten. 



The planicosta-ziphus series of the armati : they are anagenetic to 

 5** (A. scoresbyi, Simpson) ; Deroceras is catagenetic or post 5**. Micro- 

 deroceras is earlier and has a more complex suture line. Si^ijpijj, 

 armed with a sword : ziphus is evidently a mistake for xiphus = $i<t>os, 

 a sword. 



Genus, C(ELOCERAS, Hyatt, 1867 



1867, Foss. Ceph. ; Bull. Mus. Comp. Zool., V, 87, 94. 



Of the species mentioned by Hyatt, A. pettos, Quenstedt,was selected 

 as genotype by S. Buckman, Geol. Soc. LIV, 1898, 454. 



The Charmouthian species have cylindriform whorls, cratermubilicus, 

 and broad, little costate periphery. Whether certain similar shaped 

 Domerian and Whitbian species which have well costated venters are 

 descendants, or are inflated Dactyliocerates, or have passed through the 

 fibulate stage, is not always certain ; but till ontogenetic details are better 

 known they may be ranged here. Thus Ca-Zoceras =stout-whorled 

 Dactyloids. 



Result 



Genus, Cceloceras, Hyatt, 1867. Genolectotype, A. pettos, Quen- 

 stedt, Jura, xvi, 14. 



