standing out at right
angles; and lastly, when I found the whole capitulum bluntly pointed,
instead of being square on the summit, I had not the least doubt, that
it was a quite distinct species. Afterwards, I found in the _Cineras
Olfersii_ of Leach, from the South Atlantic, the same form of terga; but
within slightly more concave or furrowed, and not nearly so small, and
therefore not placed at above half so great a distance from the other
valves; and here, the carina had its usual outline, as had nearly the
scutum on one side, whereas, on the other side, it presented a new and
peculiar form, having five ridges or points, and was imperfectly
calcified; seeing this, it was impossible to place much weight in the
precise form or size (and therefore, relative separation,) of the
calcified valves; and on close examination, I found every part of the
mouth and cirri identical in Leach's _Cineras chelonophilus_ and _C.
Olfersii_, and in the common form. Therefore, I conclude, that _C.
chelonophilus_, and still more _C. Olfersii_, are only varieties; the
terga presenting the greatest, yet variable, amount of difference,
namely, in their acumination and flatness. We know, also, that in the
species of the closely allied genus of Lepas, the terga are very
variable in shape, and this is the case, even in a still more marked
degree, in _Conchoderma aurita_. Professor Macgillivray, I may add, has
come to a similar conclusion regarding the extreme variability of the
valves of this species.

As the varieties here mentioned are very remarkable, and may perhaps
turn out to be true species, I think they are worth describing in some
detail: I will only further add, that we must either make several new
species, or consider, as I have done, several forms as mere varieties.

C. VIRGATA, var. CHELONOPHILUS of _Leach_. Pl. III, fig. 2 _c_.

Atlantic Ocean, 35 deg. 15' N., 16 deg. 32' W. On the Testudo caretta.

Capitulum not above half an inch long, composed of very thin membrane,
with six bands (as stated by Leach) of faint colour; summit bluntly
pointed; valves very small, far distant from each other; the scuta are
imperfectly calcified, the central part of the umbo consisting of thick,
brown chitine, with imbedded shelly beads; terga and carina perfectly
calcified.

_Scuta_ trilobed, flat, within slightly concave, upper lobe rather more
acuminated than the lower; lateral lobe triangular in outline, twice as
wide as either the up