MYALINA. 
49 
almost straight. Front wing very small, convex. Anterior margin very long and 
very concave. Antero-inferior corner apparently so rapidly rounded as to be 
almost angular. Posterior and inferior margins continuously and regularly 
convex. Line of highest elevation arching round from the umbo to the antero- 
inferior corner, so as to be nearly parallel to the anterior margin ; the contour being 
rapidly convex over this line, spreading out flatly behind it to the margins, and 
sinking rapidly in front of it to the anterior margin. Surface marked only with a 
few very indistinct growth-lines and minute intermediate striae. Shell- structure 
probably very thin. 
Size. — Length 37 mm., breadth 43 mm., depth of one valve about 8 mm. 
Locality. — A single specimen from Lummaton is in my Collection. 
Remarhs. — Although much of this specimen is hidden, there is no doubt about 
its shape and character. Its highly lunate shape at once distinguishes it from 
every other species I know. 
5. Myalina pinnoides, Whidborne, sp. PI. IV, fig. 4. 
1889. Mttilus pinnoides, Whidborne. Greol. Mag., dec. 3, vol. vi, p. 79. 
Description. — Right valve large, triangular, oblique, recurved. Umbo small, 
acute, proximate, situated at the anterior point, and facing anteriorly. Hinge- 
margin long, slightly convex. Anterior margin very broad, oblique, and slightly 
concave. Posterior and inferior margins convex. Contour of back flatfish, 
oblique, tending to form an indistinct wing behind ; deepest near the front, where 
it curves rather suddenly, and becomes nearly perpendicular to the anterior 
margin ; marked in the centre by a slight, shallow, linear depression, which runs 
from behind the umbo to the postero- inferior part of the shell. Surface smooth. 
Shell-structure papyraceous as far as seen, but probably its outer layer is 
entirely absent. 
Approximate size. — Length 45 mm., height 60 mm., depth of one valve 7 mm. 
Locality. — There is a single specimen from Wolborough in Mr. Vicary's 
Collection.- (il.MyZ/^C 
^ . . . . . 
Bemarlcs. — This specimen is almost entirely a cast, and its characters cannot 
be very distinctly made out. The shell on the parts where it remains is very thin, 
but it seems most likely that it is only the inner layer, and that the outer layer 
has entirely disappeared. Behind the umbo there is a depression which appears 
to indicate a thickening of the hinge at this point. 
Affinities. — This is a much less arcuate shell than Myalina luna. 
It appears less elongate than Mytilus uncinatus, Eichwald,^ and has a less 
arched umbo. 
1 18G0, Eichwald, ' Lethsea Eossica,' p. 981, pi. xxxviii, fig. 7 a, h. 
VOL. II. 7 
