ORDER I PRIONODESMACEA 371 
Sub-genera: Actinopteria, Liropteria, Vertumnia, Hall. Devonian. Pteronites, M‘Coy. 
Deyonian and Carboniferous. ? Rutotia, de Kon. Carboniferous. Oxytoma, Meek (Fig. 629). 
Trias to Cretaceous. Meleagrina, Lam. Jura to Recent. 
Limopteria, Hall (Monopteria, Meek ; Myalinodonta, Paropsis, Oehlert). Anterior 
wing reduced, posterior large. Devonian and Carboniferous. 
Pteroperna, Morris and Lycett. Middle Jura. 

Fic. 628. 
Pteria contorta, 

Bac ne 
Portl. sp. Rhae- Fic. 629. Fie. 630. 
tic ; Kossen, Pteria (Oxytoma) costata, Sow. Great Oolite ; Pseudomonotis echinata, Sow. Corn- 
Tyrol. Luc, Calvados. brash (Oolite) ; Sutton, England. 
Pseudomonotis, Beyr. (Eumicrotis, Meek), (Fig. 630). Left valve flat, anterior wing 
not developed or minute. Devonian to Cretaceous. 
Cassianella, Beyr. (Fig. 631). Left valve inflated with prominent incurved beak ; 

Fic. 632. 
Fic. 631. Monotis salinuria, Schloth. sp. Red 
Cassianella gryphaeata, Miinst. sp. Upper Trias ; Alpenkalk (Norian); Berchtesgaden, 
St. Cassian, Tyrol. Bavaria. 2/3. 
the right fiat or concave, without byssal sinus; teeth small as in Pteria, but more 
numerous ; area amphidetic, wide. Trias. 
Monotis, Bronn (Fig. 632). Equivalve, compressed, radially striate, with low, sub- 

Fia. 634. 
Fic. 633. Posidonomya Becheri, Bronn. 
Halobia (Daonella) Lommeli, Wissm. Lower Culm Measures ; Herborn, Nassau. 
Keuper (Norian); Wengen, South Tyrol. 1/,. 
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, 
