CONCHOLOGY. 65 



N. Limatula. N. nitida. 



N. Isevis. N. tenuis. 



N. concentrica. N. convexa. 



N. decussata. N. Pisum. 



N. exigua. N. carinifera. 

 N. squamosa. - N. torta. 



N. gigantea. N. plicaria. 



N. navicularis.* N. proxima.* 



N. tenuisulta.* N. acuta.* 



N. my alls.* 



FAMILY XII. 



Tkigonacea. Two genera. 



1. Genus Trigonia. PI. VIII.' 



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 She 

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

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

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

 tralian seas. One living species. Fifteen fossil. 

 Trigonia pectin ata. 



2. Genus Castalia. PI. VIII. 



Animal. Body large, slightly compressed, 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 cirri for the respiratory cavity ; flamelliform and tren- 

 chant. 



Shell. Subtrigonal, equivalve, inequilateral; umbones eroded, 

 6^= 



