666 MOLLUSCA phylum vi 



Oppel; (?) Simoceras Zittel (Fig. 1293); Siemiradzkia Hyatt. Type S. (Ammonites) 



PcUoccras athlctd (Pliill.). Uppei' Callovian ; Vaclies noires, 

 Normandy, i/i. 



Fi(i. 1295. 



Physodoceras circum- 

 spmosum (Oppel). Upper 

 Jura ; Swabian Alps. i/w. 



hakeriae (d'Orb.) [Terr. Jurass. PL 149, Fig. 1, non PL 148]. Physodoceras Hyatt 

 (Fig. 1295). Type P. (Ammonites) circumspinosum (Oppel). Upper Jura. 



Family 27. Desmoceratidae ZitteL 



Discoidal moderately . involute forms, loith simple or divided ribs. These continue 

 toithout interruption across the rounded keelless venter. Constrictions or varices at 

 regular intervals. Septa finely diyitate, with aiixiliary lobes arranged in a straight roiv. 



The Desmoceratidae are slightly modified descendants of the Stephanoceratidae, 

 and preserve in youth the characters of the ancestral family. 



Subfamily A. Desmoceratinae Zittel (ixirs). 



Mostly involute shells, smooth, or with constrictions and fold-like costae without 



tubercles that commoidy follow the 

 lines of growth across the rounded 

 venter uninterruptedly. Spines 

 sometimes present as in preceding 

 family. Sutures have blunt 

 siphonal saddles, never pointed. 

 First lateral lobes shalloAver than 

 in the Lytoceratidae, the first 

 lateral saddles broader, and less 

 deeply cut by marginals. Anti- 

 siphonal lobe long, straight, and 



trifid. Lateral zygous inflections more numerous, and there are often three or more 



zygous dorsal saddles. 



Fio. 1290. 



Suluie-liiio of Dcxtiioceras latidorsatmn Midi. 

 Peite du Kliniie. 



Gault ; 



