39 
TAB. CCCCXXXI. 
Trigonia elongata. ( var . T. costata?) 
Spec. Char. Elongated gibbose subtriangular ; 
anterior side obtuse, transversely costated ; 
posterior side separated from the anterior 
by a crennulated carina, bicarinated, lon- 
gitudinally striated, striae granulated. 
Syn. Trigonia costata (b.) Lam. Hist. Nat . 
FT. pt . I. p. 64. 
Much doubt is experienced upon examining a number 
of specimens of this Trigonia, they vary so considerably 
in length, or rather in the inclination the hinge line and 
costae bear upon the large carina, and also in the form of 
this carina ; and we are strongly inclined to believe with 
Lamarck that it is only a variety of Trigonia costata 
(Min. Conch, t. 35.) The costae are rounded and pro- 
minent, they are rarely connected with the carina, 
but they are more often separated from it by a furrow. 
The carina is sometimes broad and low, sometimes it is 
elevated moderately, and at others it is very prominent 
and thin ; it is always more or less crenated. The an- 
terior side has two lesser carinse, of which that nearest 
to the hinge is the most elevated ; between them are 
many strongly erenulated ridges. The beaks are 
elegantly incurved. 
Two of the figures (1 and 2) upon this Plate are from 
specimens found at Radipole, near Weymouth and se- 
lected from among several in the possession of our very 
kind Friend M iss Benett ; at first sight they seem 
very distinct from the T costata of the Ironshot or in- 
