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Genus 35.— C ORB IS.— .Cwuzer. 



Generic Character Transverse, equivalve, without flexuosity, 



slightly depressed ; beaks small and incurved ; hinge with two 

 primary teeth, and two lateral ones, of which the posterior 

 one is nearest the cardinal teeth ; muscular impressions simple j 

 ligament external. 



Corbisfimhriata. — The Fringed Corbis. Plate XVII. fig. 

 8. Very thick, white, transversely oval, gibbous, longitudinally 

 striated, with transverse undulated furrows ; the margins crenu- 

 lated ; with depressions somewhat lanceolate. Two inches and 

 a half broad. Inhabits the Indian ocean. 



Genus ^6 ARCOPAGIA.— Zeac/i. 



Generic Character. — Transverse, equivalve ; right valve sub- 

 depressed ; umbones very small, and nearly straight ; with two 

 primary teeth in each valve, each of the larger ones being cleft ; 

 left valve with two remote lateral teeth, that on the anterior 

 slope large, with a sinus betwixt it and the margin for the recep- 

 tion of the lateral tooth in the opposite valve ; muscular impres- 

 sion extremely large, and defined by a deep irregular groove ; 

 near its lower centre are several strong punctiform marks ; mar- 

 gin very broad, and well defined and glossy; ligament subex- 

 ternal. 



Arcopagia crassa. — The Thick Arcopagia. Plate XVII. 

 fig. 9. Suborbicular, strong, thick ; upper valve flat ; with 

 coarse, thick-set, transverse striae ; pale yellow, radiated longi- 

 tudinally ; inside white, with a large patch of yellow or pink ; 

 muscular impressions very deep. One inch and a half long 

 Inhabits the British seas. 



Genus 37.— TEhLmiBES.— Lamarck. 



Generic Character. — Transverse, inequilateral, flattened, a liu 

 tie gaping laterally ; beaks small, and sub-depressed • margin 

 plain, irregular, but not inflected ; two divergent primary teeth 

 in each valve, and two lateral teeth, which are somewhat obso- 

 lete, in one valve. 



M 



