ORDER I 



PRIONODESMACEA 



371 



Sub-genera: Actinoptcria, Liropteria, Vcrtuinnin, H.ill. Devonian. /'/.,,////..<. M-C..V. 

 1 1, -\ nniaii an.l ( larboniferous. .' Hutotia, de Kon. Carboniferous. Oxytoma, Meek (Fig. 629). 

 Trias to Cretaceous. Melcayrina, Lam. Jura to Ren nt. 



Limopteria, Hall (Monopteria, Mr-k : Mii<i!inil<>iitti, /'-//--/y/x/X 

 whig ivduced, posterior largp. ]>pv<>nian and 

 Pteroperna, Morris ami l.vi-pit. Middlp Jura. 



Fia. 628. 



I'ti r'ui /iiiitnii", 



Portl. sp. Rhae- 

 tic : Kiissen, 



Tyrol. 



Fio. 



rt''i-'<'i (i>.<-,/ti,,it) cnttfitti, Sow. Great Oolite ; 

 Luc, Calvados. 



Fio. 630. 



Pmulomonotis echin"'". Si\v. 

 brash (Oolite) ; Button, 



('urii- 



Pseudomonotis, Beyr. (Eumicrotis, Meek), (Fig. 630). Left valve flat, anterior wjng 

 not developed or minute. Devonian to Cretaceous. 



Cassianella, Beyr. (Fig. 631). Left valve inflated with prominent incurved beak ; 



Cassianella gry t 

 St. Cassian, Ty 



FIG. 631. 



Miinst. sp. Upper Tri 



FIG. 032. 



Monotis salinarin, Schlotli. sp. H. I 

 Alpenkalk (Norian) ; Berchtesgaden, 

 Bavaria. 2/3. 



small as in Pteria, but more 



the right flat or concave, without byss-il sinus; 

 numerous ; area amphidetic, wide. Trias. 



Monutis, Bronn (Fig. 632). Efj[iiivHlvi', compressed, radially striate, with low, sub- 



FlG. 633. 



Halolriii (l><i<,,,.-ii") LomoMU, Wissm. Lower 

 Keuper (Norian) ; Wengen, South Tyrol. 



Fia. 034. 



Posidonomya Jiecheri, Bronu. 

 Culm Measures ; Herborn, Nassau. 



Vi- 



central beaks; anterior wing indistinct, rounded; posterior wing short, truncate or 

 oblique. Trias. 



Halobia, Bronn (Daonella, Mojs.), (Fig. 633). Equivalve like Monotis, but the 

 anterior wing only represented by a smooth non-projecting area (Halobia), or both 

 wings absent (Daonella). Abundant in the Trias. 



Posidonomya, Bronn (Ablacomya, Steinm.), (Fig. 634). Equivalve, thin, compressed, 



