CONCHOLOGY. 65 
N. Limatula. N. nitida. 
N. levis. ‘ 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. myalis.* 
FAMILY XII. 
Triconacrd. Two genera. 
1. Genus Trigonia. Pl. VIII." 
Animal. Entirely unknown. 
Shell. Subdtrigonal 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. 
Trigonia pectinata. 
2. Genus Castalia. Pl. 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* 
