TEREDO. 215 
been termed salivary glands, and may perhaps be such. The 
oral aperture is subtriangular. The foot im the hving 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, sprmging 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 im haying 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 Phol/as, 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 branchize 
being inclosed in the usual bivalve portion, they are placed in 
