648 



MOLLUSCA 



PHYLUM VI 



LS 



entire. Shells have a line of nodes on the ventro-lateral angles, and the venter is 



invariably smooth and convex. 



Includes Tirolites (Fig. 1235) and Mctatirolites Mojs., from the Alpine Trias and 



from Idaho. The subfamily of Clydonitinae has sutures 

 similar to Tirolites, but costae interrupted on the venter, 

 which is often channelled. Includes Clydonites and Eremites 

 Hauer ; and Edolcites Mojs. Trias. 



Subfamily C. Dinaritinae Mojsisovics ^pars). 



Sutures resembling Tirolites in having only two broad 

 saddles, one pair of first lateral lobes, and incomplete lobes 

 at the umbilicus. Shells smooth, or with coarse_ folds 

 most prominent at the umbilical shoulders ; sides more or 

 less flattened or jilanoconvex, and venter rounded. 



Dinarites Mojs. ; Guceoceras Diener. Trias. 



Subfamily D. Buchitinae Hyatt. 



Primitive forms similar to Celtitinae, with smooth 

 elevated venter ; more specialised shells with slight keel on 



Fig. 1235. 



Tirolites cassianus (Quenst.) the narrow venter, and simple costae or folds on the sides. 



Lower Trias ; GronR.s-Hof, near Sutures have entire outlines, or lobes but slightly denti- 

 st. Cassian, Tyrol. ' & •' 



LUilated ; and when the saddles are comj^letely divided 

 Sutures otherwise similar to those of Dinaritinae, and the 

 young have a Dinarites stage. Antisijihonal lobe entire and bifid in some forms. 

 Buchites, Helictites, Phormedites, Parathisbites and Glyphidites Mojs. Trias. 



their marginals are small. 



Suljfamily E. Arpaditinae Hyatt. 



Dift'ers from the Buchitinae in the tendency to form channelled venters bordered 

 by two ridges, which may be either tuberculose or smooth. 



Arpadites (Fig. 1236), Klipsteinia, Dittmarites, Muensterites, Steinmannites, Daph- 

 nites, Dionites, Drepanites, Heraclites, Guembelites, 

 Cyrtopleurites and Acanthinites Mojs. Trias. 



Subfamily F. Trachyceratinae Hyatt. 



Discoidal and involute shells with well-defined and 

 often profusely tuberculated costations which are 

 interrupted on the ventral aspect by a smooth zone 

 or channel. This may in some specialised forms 

 become a distinct channel bordered by tuberculated 

 ridges. Lobes and saddles completely divided by 

 marginals, but these do not become very long nor 

 complex. 



Distichites, Trachyceras (Fig. 1237), Protrachyceras (Fig. 1238), Anolcites, Sand- 

 linyites, Sirenites, Anasirenites, Diplosirenites and Glionites Mojs. (Figs. 1239, 1240). 

 Trias. (?) Heqyerites Pompeckj. Rhaetic. 



Fig. 1236. 



Arpadites cinensis Mojs. Keuper ;■ 

 Esino, Lombardy. 



Subfamily G. Chorlstoceratinae Hyatt. 



Discoidal anmioniticones in primitive forms, becoming uncoiled phylogerons, and 

 finally even complete baculiticones in the most specialised species. Sutures also 



