173 
shells, of different genera, being combined in this one shell : — “ Une 
espece de coquilles des plus rares dans le regne des fossiles, qu’on ne sait 
encore sous quel genre elle pourroit etre convenablement rangee, vu 
qu’elle tient en meme terns, beaucoup du musculite, de l’arche et de la 
conque de Venus. Elle approche fort du musculite par le raport de sa 
longueur a la largeur ; elle ressemble a un arche, par une petite emi- 
nence, ou une espece de petite plate forme qui se trouve entre les deux 
bords de la charniere : et les bords, qu’elle a un peu convexes d’un coffi, 
lui donne la ressemblance avec la conque de Venus.” Monumens des 
Catast. Tome n. p. 66. 
Notwithstanding the combination of the characters of the muscle, ark, 
and Venus, as observed by Walch, and to which may be added those of 
the cockle and the tellen, these shells vary so much from every other, 
as to render their description difficult. On first view, the shell appears 
reversed : the anterior end, on which, particularly in the Venuses, the 
area surrounding the cartilaginal depression is disposed, and which is in 
general flat, as if it were truncated, is, in these shells, considerably ex- 
tended out ; whilst the beaks of the shell are turned towards the anterior 
side, leaving the posterior side with no cordiform impression, but having 
all the appearance of the anterior side, in the shells of the Venus kind. 
Bruguiere has, I understand, described, in V Encyclopedic Metho- 
dique, four species of this genus ; but, being unable to obtain this work, 
I am uninformed with which of the species he is acquainted. 
The first information which I gained respecting the generic character 
of these shells, was from a fossil purchased from Mr. Strange’s collec- 
tion ; in which the left had so slipped from the right valve, as very fully 
to display the structure of the hinge. Bruguiere having been so fortu- 
nate, as, by clearing a valve, to discover the kind of hinge which it pos- 
sessed, found it necessary to form a genus for the reception of these 
shells, and named it Trigonia, from the form which generally belonged 
to the species then known. 
But, as in my specimen, so in Bruguiere’s, it was the hinge part of 
