660 



MOLLUSCA 



PHYLUM VI 



In another group of tlie Amaltheinae, tlie young usually have gibbous volutions with 

 a single row of nodes, which either persist, or are followed by a bispinous stage, and 



inner ends of the short costae also become 

 tuberculated. Venter smooth at first, and 

 may remain so or may have a solid keel. 

 Costae single, and usually bend at ventro- 

 lateral angles tOAvard the keel, but do not 

 cross the venter except in late stage of 

 Pseudotrojntes. Haplopleuroceras and 

 Dorsetensia Buckm. ; Psexidotroioites 

 Canav. ; Ganavarites Hyatt. Type C. 

 (Arietites) discretum (Canav.). Lias to 

 Inferior Oolite. 



The Amaltheinae are usually classed 

 as derivatives from the Arietitinae, but 

 this is doubtful. Oxynoticeras Hyatt 

 (Fig. 1276) from the Ijias, is classed by 

 most writers with the Amaltheidae, 

 although Hyatt regarded it as a member 

 of the Arietitinae. In this genus the 

 shells are compressed and more involute than in the Arietidae, with narrower and 

 more acute keeled venter, but no ventral channels. Sutures have extended and 

 liighly modified auxiliary inflections ; keel hollow in adult of some species. Lower Lias. 



Fi(i. 1276. 



Oxynoticeraa oxywitum (Quenst.). 

 (j3) ; Wiirtemberg. 



Lower Lias. 



Subfamily B. Hammatoceratinae Buckman. 



Discoidal forms with single or bifurcated costae, keeled and often channelled 

 Young similar to those of the Harpo- 

 ceratinae in compressed forms. Keel 

 hollow. 



Cycloceras and Hammatoceras Hyatt ; 

 Lillia Bayle ; Haugia, Polyplechis, Chart- 

 ronia, Denckmannia Buckm. ; Zurcheria 

 Douville. 



Upper Lias and Inferior Oolite. 



The Hammatoceratinae have usually 

 been classed as near relatives of the 

 Arietitinae but their systematic position 

 should probably be in the Amaltheidae, 

 with which they show near affinities in 

 form and septation. 



Buckman placed two genera or sub- 

 genera of this subfamily in a separate 

 group '■^ Sonniniinae." /Son?!^^ includes 

 discoidal forms with a keeled but not 

 channelled venter, and sides with coarse 

 bifurcated costae diverging from a row 

 of nodes along the median line of the 

 rounded sides and continued internally 

 by single costae. Witchellia has nodes 

 only in the young, and costae become 

 single or only slightly confluent. Sonninia Bayle {JVaagenia Bayle) (Fig 

 Jl'^itchellia Buckman. Inferior Oolite. 



venters. 



B 



Fic. iL'vr. 



SonnUiia so}t'erhyi (Miller). Middle Dogger ; 

 (after SteinmaTin and Diiderlein). 



Lorraine 



1277); 



