TEREDO. 215 



been termed salivary glands, and may perhaps be such. The 

 oral aperture is siibtriangular. The foot in the living animal 

 appears bluish hyaline, but when the moisture is absorbed it is 

 muscular and coriaceous, attached to the body by a thick 

 powerful cylindrical pedicle, and in its centre, the terminus of 

 the hyaline stylet is visible ; the form of its basal area is that 

 of the anterior gape, which is of a diamond figure, with its 

 angles placed vertically and transversely, but the transverse 

 axes are longer than the vertical. A pair of yellowish-white 

 spatulate appendages are fixed to the posterior extremity of 

 the body. In this animal, besides the anterior and posterior 

 apertures of the shell, there is a rather extensive oval orifice on 

 the dorsal surface of the shell, which is covered by a thick sub- 

 circular tough skin, springing from the internal part of the 

 anterior end of the mantle, which appears to have the val- 

 vular function of closing the orifice ; but it will be mentioned 

 again. 



These are the only features of the animal which are visible 

 without dissection. A bivalve animal consists of the shell, 

 soft parts, and the hinge, which latter organ has caused some 

 misconceptions, which I will endeavour to remove. In this 

 species it is nearly similar to that of Pholas ; the valves arti- 

 culate on a thin genuine cartilage, which is a secretion from 

 glands; on each side the anterior dorso-lateral part of the 

 body the denticular appliances are wanting in one valve, and 

 in the other there is only a short blunt tooth ; the ligament 

 is a united production of the glands just mentioned, and the 

 mantle ; it may be considered to be more external than inter- 

 nal, and only differs from Pholas in having one, the upper, 

 instead of two layers of transverse fibres, strengthened and 

 covered as in that genus by the anterior end of the mantle 

 being reflected on it, but it is not fortified by testaceous plates. 

 We have here all but the hinge of Pholas, and taking the shell 

 as far as its circumscribed volume extends, we find it nearly 

 similar, in having the curved subumbonal internal apophyses, 

 the single post-medial adductor, and the long tubular mantle 

 fixed to the auricles ; but instead of the viscera and branchise 

 being inclosed in the usual bivalve portion, they are placed in 



