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 ' veritable 

 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 charniere, 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 testaceous plate; the use of 



N 2 



