Lamarck’s Genera of Shells. 321 
8th Family. t 
TRIiGONIANA. (2 Genera.) 
Cardinal teeth lamellar, transversely striated. 
The shells of this family which embraces but two genera, are 
free, regular, equivalve, inequilateral, ribbed longitudinally or 
transversely, and are remarkable by their lamellar and trans- 
versely striated cardinal teeth, which differ from those of the 
arcacea, by the strie being on separate laminz, instead of being 
on the hinge itself. 
1. Trigonia*. 
Shell equivalve, inequilateral, triangular, sometimes subor- 
bicular. Cardinal teeth oblong, flattened at the sides, diverg- 
ing, transversely furrowed ; two on the right valve furrowed on 
both sides, four on the other furrowed only on one side. Liga- 
ment external, marginal. 
The trigoniz are regular, free, very inequilateral sea-shells, 
and all, except one species, only known in the fossil state. 
Type. Trigonia pectinatat. 
» Shell suborbieular, radiately ribbed ; internally pearly; ribs 
prominent, ventricose, rather rugged ; margin plicate. Exter- 
nally it resembles a pecten without ears. New Holland. Re- 
cent, 15fossil species. PI. vi. Fig. 68. 
2. Castalia t. 
Shell equivalve, inequilateral, triangular; beaks eroded, 
curved backwards. Two lamellar cardinal teeth, transversely 
striated ; one’posterior, distant, shortened, sub-tri-lamellar ; the 
other anterior, elongated ; lateral ligament external. 
The castalia resembles a trigonia in appearance, but differs 
from it by the number and situation of its teeth, which have 
more resemblance to those of the unio, between which and the 
trigonia it seems to be iatermediate. It appears to be a river 
shell. 
* From rec, three, and ywva, an angle: 
+ Comb-shaped, resembling a pecten. 
$A name infabulous history, The daughter of Achclous, who was changed 
into 3 fountain, 
Vou. XIV. Y 
