remarkably acuminated; the vesiculae
seminales are unusually small, and enter only for a short distance into
the prosoma; the testes are large. The ovarian tubes are of large
diameter; the ova are nearly spherical and large, namely, 9/400ths of an
inch in diameter; they are not numerous, and lie in single layers in the
two lamellae. The ovigerous fraena are well developed, and lie under the
scuta; one I measured was 5/100ths of an inch in length and 2/100ths in
width; the margin is obliquely truncated and slightly sinuous. This
species breeds late in the autumn, and even in mid-winter; I have
examined a specimen from Cornwall with ova containing larvae, taken on
the 26th of October; again, in another specimen from Belfast, sent to me
by Mr. Thompson, taken in January, there were ova in the lamellae, and
therefore no doubt impregnated; and on February the 12th I received from
Mr. Peach, from Cornwall, specimens so very young that they must have
become attached during the first days of the month.

_Varieties._--The specimens from near Naples, (which I owe to the
kindness of the Rev. F. W. Hope,) are somewhat larger, and differ
slightly from those of Britain: they form, I imagine, the _S. Siciliae_
of Chenu. After carefully examining them internally and externally, I
think it is quite impossible to consider them specifically distinct, for
although in several specimens, the valves were placed a little further
apart from each other,--the upper latera a little more elongated,--the
carinal latera rather narrower in their upper half,--the infra-median
latera rather more rounded,--and, lastly, in the scuta, the tergal
margin extended almost in the same line with the lateral margin;
nevertheless in other specimens, I could perceive no difference
whatever. It is, however, remarkable that in several full-grown
Neapolitan specimens there were no Complemental males, whereas I have
never seen a single full-grown British specimen without such being
present. In some specimens in the British Museum, without any given
locality, I have observed considerable variation in the breadth of the
carinal and rostral latera.

COMPLEMENTAL MALE. Pl. V, figs. 9-14.

When first dissecting _Scalpellum vulgare_, I was surprised at the
almost constant presence of one or more very minute parasites, on the
margins of both scuta, close to the umbones: these are represented, but
rendered darker and therefore more conspicuous than in nature, in the
draw