896 Rerort or tae State Groxoaist. 
Type, Platidia anomioides, Scacchi (sp.). 
Distribution. Recent (Lusitanian, Californian, Magellanian, 
Caribbean and Transatlantic Provinces). 
Megathyris, d’Orbigny. 1547. 
Synonym; Avgiope, Deslongchamps, 1842. 
Shells transversely elongate; hinge-line long and straight, 
equaling the greatest diameter of the valves. Cardinal area well 
developed on both valves Foramen 
- large, oval, deltidial plates*small. In 
the pedicle-valve there is a median 
septum and two low lateral septa. 
Brachial valve with prominent car- 
Gere: Sate ae ee dinal process, and three or five septa 
plates; g, crura; 1, lobed extension of lying in front of the visceral region, 
cee ea Poa Of these, one septum is median. 
Brachidium consisting of a simple continuous lamelz with broad 
oral processes and divided into four lobes by the median and first 
pair of lateral septa. The brachial disk is likewise divided into 
four lobes. 
Type, Megathyris decollata, Chemnitz (sp.). 
Distribution. Jurassic— Recent (Lusitanian Province). 
Cistella, Gray. 1850. 
Exteriorly like Mxearnyris. Interior of the valves with 
median but no lateral septa. Brachial lamella bilobed by the . 
median septum to which it is partially attached. 
Fies. 636-628. Cistella cuneata, Risso (sp.). Davipson. 
Type, Cistella cuneata, Risso (sp.). 
Distribution. Cretaceous— Recent (Boreal, Lusitanian and 
Caribbean Provinces). 
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