PHOLAS. 179 
it is extraordinary, even in late malacological works, to find it 
described as obscure and rudimental, and M. Deshayes, in his 
comment on Pholas in the last edition of Lamarck, mentions 
the hinge as scarcely existing, and not being a ‘ véritable 
ligament ’—how different from the fact! If there is a genus 
better provided than any other of the bivalves with ligamental 
appendages, it is Pholas. 
The hinge of Pholas dactylus has very slight traces of denti- 
cular assistance; it nevertheless works en charniére, in a 
circumscribed space, to which it is confined by powerful liga- 
ments, and though somewhat different in its component parts 
from the usual configuration, it does not in its functions 
materially differ from those of the ordinary bivalves ; it has a 
strictly internal cartilage, which is laminar, of small volume, 
oval shape, and light yellow colour; it is fixed on the internal 
portion of the convexity of the valves, termed the hinge, which 
articulates, imbedded in the thin plates of the cartilage. The 
ligament succeeds ; it consists of two parallel plates, between 
which is a considerable interspace of strong, close-set, white, 
elastic transverse threads, the one fixed more externally to the 
inner side of the reflected dorsal cellular excrescence, the 
other, below it, to the internal commissure of the two valves ; 
thus forming a powerful ligament that allows them the usual 
movement of the ordinary hinge: on this is added a third 
ligamental apparatus, which may be termed accessorial, to in- 
crease the strength of the hinge, and which is formed by the 
reflection of the tough end of the mantle issuing between the 
anterior points of the valves in an elongated oval form, and 
covers the transverse threads of the outer layer of the liga- 
ment; it is firmly secured by throwing out filaments which 
enter the dorsal cells of each valve: this production of the 
mantle is further fortified by two thin, flexible, suboval testa- 
ceous plates, supported by a subtriangular rest ; these appen- 
dages are exudations from the reflexed mantle. The posterior 
part of the valves, as is usual in elongated shells, has the 
common continuous membranous ligament produced by the 
protrusion of the edge of the mantle, with the addition, in 
this species, of a long thin linear testaceovs plate; the use of 
N2 
