140 Ona Species of Teredo found in Aberdeenshire. 
of a pholas, but without accessory piece. Each valve is semi- 
circularly curved, and, as in the other species, may be de- 
scribed by comparing it to a valve of Pholas crispata, ex- 
tremely shortened in its antero-posterior direction, and 
lengthened from the umbo to the ventral portion, which runs 
out into a narrow process. Although very minute, its mark- 
ings are very distinct, and extremely beautiful. From a 
rounded glossy supra-umbonal prominence, having an ante- 
rior faint plait, the frontal margin, directed forwards and 
laterally, is a little concave, and divergent ; the anterior out- 
line forms an acute angle with it, proceeding directly back- 
wards, and is then directed downwards at aright angle. The 
dorsal margin, at first concave, rises into a prominence, and 
then forms a very thin-edged rounded, reflexed lobe, beyond 
which the outline is directed downwards and forwards to the 
anterior point of union of the valves. Viewed from before, 
the ring thus formed is sub-rhomboidal, with a sinus above, 
formed by the separation of the frontal margins, and oc- 
cupied by a strong transverse muscle. Seen from behind, 
it is roundish-ovate, narrowed above. On each valve ex- 
ternally, from behind the umbo to the ventral margin, is a 
distinct convex ridge, accompanied by a’shallow groove ; ante- 
rior to which, on the angular upper and anterior part, are 
about twenty-five strize or lamellz, parallel to the lower mar- 
gin of this part, and continued behind into much finer lines, 
occupying the very narrow space between the ridge and the 
anterior margin. Behind the ridge, the valves are faintly 
striated parallel to the margin. In fact, in this, as in all the 
other species known to me, all the striz are so arranged, as 
they are also in the Pholades. The interior is glossy, and 
presents under each umbo a very long, arcuate, linear pro- 
cess, considerably flattened, resembling a fine bristle, and ex- 
tending nearly to half the diameter of the ring. The palmules 
are large, very broadly pyriform, subobcordate, very thin, 
concave, tapering rapidly into a styliform pedicle, and having 
on their inner face a longitudinal ridge, not medial, continu- 
ous with the pedicle. 
The species of Teredo are very inadequately described by 
