316 Mr. W. Clark on the Pholadidae. 



the palpi on each side are so nearly similar to those of P. dac- 

 tylus as to require no observation ; the siphonal sheath when ex- 

 tended is double the length of the shell. The liver is darker 

 than in the last species. 



Pholas Candida, Linnseus. 



Animal conically elongated from the anterior end to the pos- 

 terior axis of the cone. The body, sheath and mantle are a pale 

 red-brown, but when divested of the e])idermis, of the palest hya- 

 line tinged with brown. The mantle as usual is closed, except 

 the aperture for the foot, and being produced into a sheath that 

 is proportionately shorter than in its congeners ; the siphons are 

 of the same length, and both are cirrhated at their orifices, the 

 only example in this respect that we know of amongst the Pho- 

 lades; the branchial with about twelve whitish brown rays, of 

 deeper tint towards the base, and between some of them one or 

 two smaller, but not fimbriated ; the anal has about eight short 

 pale rays. Some authors describe papillae on the tubes ; our spe- 

 cimens only showed minute sand-like points, which we think are 

 due to the epidermis. The foot is much narrower, more elon- 

 gated and pointed than in any of its congeners, and fixed to the 

 body by a compressed pedicle, of a pale hyaline in some animals, 

 and fiaky bluish white in others. All the other organs exhibit no 

 particular variation from those of P. dactylus. 



I have so fully entered on the boring qualities of the Pholades 

 in the January Number of the 'Annals^ for 1850 as to require 

 no remarks. The Pholades are generally excavators and inha- 

 bitants of rocks, chiefly the red sandstone on the South Devon 

 coast, but the P. dactylus and P. Candida often burrow and pass 

 their existence in pure sand at the back of the Warren and 

 Cockle Sands at Exmouth, where the finest and most delicately 

 sculptured individuals are found, surpassing in beauty the rock 

 specimens. Having concluded my remarks on the external 

 organs of the Pholades, I shall now consider the anatomy of 

 the P. dactylus, connecting with it the parts of the shell that 

 relate to the hinge, cartilage, ligament, curved subumbonal 

 apophyses, and other accessories : for reference, and to prevent 

 confusion, I have distributed the matters to be considered into 

 distinct sections. 



The Hinge. 



The hinge of the Pholades appears not to be well understood, 

 and has not received the investigation that has been so liberally 

 bestowed on the terebrating powers of the animal ; it is extraor- 

 dinary even in late malacological works to find it described as 



