164 MYADA. 
in a perfectly fresh state by Mr. Howse, of Newcastle-on- 
Tyne, who kept it alive several days; it was taken off the 
Fern Islands, on the coast of Northumberland, in deep water, 
in March 1852. It is closely allied to Mya, from which it 
differs in having a narrower foot, with a byssal groove; there 
is also a more developed tooth, and the ligament is much 
more external. But it is still closer to the genus Savicava, 
of the Gastrochenide, scarcely differing therefrom ; the hinge 
of which is all but identical, having the small conical tooth m 
each valve ; the adductor, pallial and siphonal cicatrixes nearly 
agree in shape, colour, and position; the character of the foot 
is similar, and many of the Saxicave are often found with as 
proportionately large posterior and anterior ventral gapes : the 
principal difference is in the aspect of the tubes of the two, 
which in this species is the counterpart of that of Mya truncata, 
whilst in Gastrochena and Sawxicava they appear as two tubes 
soldered together, showing sometimes the real divisional Ime 
marking the extent of the internal wall between them, and 
sometimes only an apparent depression on the common sheath. 
This comparison of the two genera would appear to show that 
the appellation of Panopea to our unique British species is 
almost superfluous, and that it might have merged in the 
Myade or Gastrochenide. 
MYADA. 
This family only contains the genus Mya, with a very few 
species, Lutraria being merged in it; it is allied to the Pho- 
lades by the characters of the branchie, the closure of the 
mantle, and the powerful siphonal apparatus; the generalities 
of the anatomy scarcely differ. The so-called Lutrarie have 
been associated with the Mactride, but they have very little 
similarity, except in the shape of the foot, and the triangular 
or V-shaped tooth; the mantle of the one is entirely closed 
ventrally, and has exceeding long siphons; in the other it is 
open, as in the Veneres, with very short tubes. 
