448 



MOLLUSCA 



PHYLUM VI 



Subf'enera: AcHnopteria, Lciopteria, Vertumnia Hall. Devonian. Ptcrondes M'Coy. 

 Devonian and Carboniferous. ? rMtotia de Kon. Carboniferous. Oxytoma Meek (Fig. 678). 

 Trias to Cretaceous. Mclcagrina Lam. Jura to Recent. 



Lmwptera Hall {Monopteria Meek ; Myalinodonta, Paropsis (Elilert). Anterior 

 wing reduced, posterior large. Devonian and Carboniferous. 



Fio. 677. 

 Pleria contort a 

 (Portl.)- Rliae- 

 t i c ; K (i s s e n, 

 Tyrol. 



Fig. G7S. 



Fleria {Oxytoma) costata Sow. Great Oolite ; 

 Luc, Calvados. 



Fig. 079. 



I'seudomonotis ecliinata Sow. Corn brash 

 (Oolite) ; Sutton, England. 



Pteroperna Morris and Lycett. Middle Jura. 



Pseudomonotis Beyr. {Eumicrotis Meek) (Fig. 679). Left valve flat, anterior wing 

 not developed or minute. Devonian to Cretaceous. 



Gassianella Beyr. (Fig. 680). Left valve inflated with prominent incurved beak ; 



Fi(i. 680. 



Cassianella gryphacata (Munst.). Upper Trias ; 

 St. Cassian, Tyrol. 



Fig. 681. 



Monotis salinaria (Schloth.). Red 

 Alpenkalk (Norian) ; Berchtesgaden, 

 Bavaria. 2/3. 



tlie liglit flat or concave, without byssal sinus ; teeth small as in Pteria, but more 

 numerous ; area amphidetic, wide. Trias. 



Monotis Bronn (Fig. 681). Equivalve, compressed, radially striate, with low, sub- 

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

 oblique. Trias. 



HaloUa Bronn (Daonella Mojs.) (Fig. 682). 'Equivalve like Monotis, but the 



Fig. 082. 



Fig. 083. 



Hdluhia (^Daunella) lommrll Wissm. Lower Keuper (Norian) ; Posidonomya hecheri Bronn. Culm Measures; 

 Wengen, South Tyrol. Herborn, Nassau, i/i- 



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

 wings absent {Daonella). Abundairt in the Trias. 



