110 THE ROTIFERA. 
aquarium, in September 1854. Its manners agreed with those of the larger Coluri, 
shutting itself within its valves, and that so stubbornly, as to die rather than open 
them. Lately I have received specimens from Mr, Hood, found in marine tide-pools in 
the Firth of Tay; and have taken many in Torbay. 
Length. Of lorica, ;1, inch ; of foot and toe, ;4,, inch; total extended, 1, to 54, inch. 
Habitat. Marine pools in Forfarshire and Devonshire ; domestic aquarium (P.H.G.). 
Very recently specimens of what I suppose M. dulcis, Khr., have been sent me, 
from fresh water, by Mr. Lord of Rawtenstall. The lorica is acute, instead of obtuse, 
behind.—P.H.G.] 

Genus MYTILIA, Gosse, gen. noy. 
(GEN. CH. Body ovate ; lorica as in Colurus, but the head and neck habitually 
protruded, as well as the whole foot ; no frontal hook.—P.H.G.] 
M. TaviIna, Gosse, sp. nov. 
(Pl. XXVI. fig. 8.) 
[SP. CH. Eyes two, frontal, wide apart. Marine. 
The lorica is essentially similar to that of Colurus (though the facies of the animal 
is quite different), being a shell of two lateral valves, like that of a mussel, unbroken 
on the dorsum, descending on each side, and open all along the venter. Behind they 
are patent, where the thick foot emerges ; but their edges approach, or even oyerlap, as 
in Pterodina, at the pectoral front. A massive head, and an equally thick, distinct neck, 
both about equal to that part of the trunk that adjoins them, are normally projected 
from the lorica, and not, as in Colwrus, concealed between the valves. As there is, 
moreover, no trace of the hood, or hooked plate, that shields the face in kindred forms, 
the difference of aspect is very marked, and one of the Iloricate forms is involuntarily 
suggested.! This is augmented by the circumstances, that the foot is long and thick, 
especially at its base, that it tapers there gradually from the thickness of the trunk, and 
that it is habitually carried in the line of the body. Whereas, in Colwrus and Monura, 
it is much smaller than the visible body, is usually projected at a sensible angle, and 
appears to come out between the ventral edges of the valves. The lorica, too, is of 
much less depth in proportion to its length; for, whereas, in Colwrus the depth to the 
length may be about 2: 8, in Mytilia it is about 2:5. It is obliquely truncate at the 
hind margin, the lateral edges diverging thence till they meet at the pectus. The body, 
which is arched on the dorsum, diminishes along the lumbar line, and forms a minute 
conical projection, representing a true tail, behind which the cloaca opens, whence the 
foot proceeds, in a similar ratio of diminution and in the same line, for a considerable 
length, terminating in two stout pointed toes, often jerked widely apart. Hach is per- 
meated by the usual mucus-gland, long, thick, and clavate. The internal structure is 
with difficulty defined. The extreme restlessness of the creature, combined with its 
minuteness, renders an examination during life almost impossible ; and, after death, the 
outlines of the delicate organs become blurred, and soon obliterated. I believe I have 
perceived, on repeated occasions, and in many specimens, two minute eye-specks at the 
front, rather wide apart. The mastax is comparatively large, and the trophi normal 
(as in fig. 8c). But the whole interior is almost opaque from granulation, and so, very 
difficult to penetrate. 
It is a pretty little creature, sprightly and attractive, with much in its manners and 
ways that reminds us of its kindred Coluri, one of which, C. amblytelus, is its constant 
1 T cannot avoid a lurking suspicion that under Ehrenberg’s figure of Distemma marinum may haye 
lain Mytilia tavina, notwithstanding discrepancies. 
