CONCHOLOGY. 



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N. concentrica. 

 N. decussata. 

 N. exijua. 

 N. squamosa. 

 N. gigantea. 



N. convexa. 

 N. Pisum. 

 N. carinifera. 

 N. torta. 

 N. plicarla. 



FAMILY XII. 

 Trigonacea. Two genera. 



1. Genus Trigonia. 

 Animal. Entirely unknown. 



Shell. Subtrigonal or suborbicular, thick, regular, equivalve, 

 inequilateral; summits but slightly prominent, little flexed, ante- 

 rodorsal ; hinge complex, dorsal, dissimilar ; two thick oblong teeth 

 joined angularly under the summit, strongly furrowed upon the 

 right valve, penetrating into two excavations of the same form, 

 also furrowed, in the left valve ; ligament postapicial ; two distinct 

 muscular impressions, not united by a band. Inhabits the Aus- 

 tralian seas. One living species. Fifteen fossil species. 

 Trigonia pectinata. 



2. Genus Castalia. 



Animal. Body large, slightly compresssed, or moderately thick, 

 more or less oval ; mantle with thick edges, simple or broken, 

 open in all its circumference except towards the back ; a kind of 

 small, incomplete tube, furnished with two rows of somewhat 

 elongated cirrhi for the respiratory cavity ; flamelliform and tren- 

 chant. 



Shell. Subtrigonal, equivalve, inequilateral ; umbones eroded, 

 covered with epidermis, and flexed anteriorly ; hinge with two 

 lamellar teeth transversly striated, one distant, posterior and short- 

 ened, the other anterior, long, and lateral ; ligament exterior. 

 Habitation unknown. One species. 



Castalia ambigua. 

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