COLURID. 101 
Family XVI. COLURIDA. 
[Body inclosed in a lorica, usually of firm consistence, variously compressed or de- 
pressed, open at both ends, closed dorsally, usually open or wanting ventrally ; head 
surmounted by a chitinous arched plate or hood; toes two, rarely one, always exposed. 
The arching hood over the front, looking, in a lateral view, like a thin hook, movable, 
and so distinguished from the ‘ glory-crown ” of Stephanops, always conspicuous, is the 
most notable mark of this family, in which I propose to unite the mostly flat Metopidie 
with the high-backed Coluri. As no subdivision above species exists in nature, but all 
(as Genera, Families, Orders, and Classes) are arbitrary collocations, made simply to 
facilitate the study of the species, which alone is natural history ; it follows that the 
more constant, and the more obvious, the characters on which we found our Divisions, 
the better. Hence I would not choose the form of the trophi, the presence or position 
of the eye-specks, or the distribution of the cilia, for distinetion—if I could get others ; 
because all these are found, in practice, so very difficult to determine. The existence of 
eyes in some Coluri and Metopidia, for instance, is so very uncertain and indetermin- 
able, that I incline to agree with Dujardin in rejecting some of Khrenberg’s genera. The 
distinction between Lepadella, Metopidia, and Squamella, is more than doubtful; while 
in Metopidia and Colwrus, individuals of indubitably the same species are found, some 
displaying eye-specks, and others in which no search detects them.—P.H.G.] 
Genus COLURUS, Ehrenberg. 
(GEN. CH. Body swbglobose, more or less compressed ; lorica of two lateral plates, 
open in front, united on the back, gaping behind, and (in general) wholly so up the 
belly ; frontal hood in form of a hook, not retractile ; foot permanently extruded, of 
distinct joints, terminated by two furcate toes. 
A very familiar group, of minute dimensions, agreeable form, and sprightly action, 
the Coluri give the impression of being, while sub-cireular in lateral outline, very thin 
in transverse diameter. This, however, is an illusion, arising from their being most 
frequently presented to the eye in the lateral aspect. When we do catch a glance at one 
in turning or swimming, we see that the body is moderately broad, ventricose, and even 
globose in the middle. The lorica consists of two glassy shells, each a segment of a 
hollow sphere, which are, normally, soldered edge to edge, at the fore-back, and begin to 
gape at the loins, the cleft then passing round behind, usually widening for emission of 
a stout foot, and passing up the belly to the front, by which time it has generally become 
as wide as the body itself. So constructed it may be imagined to be highly expansile, 
and in fact we observe that its width is constantly increasing and diminishing. The 
fore edges of the two plates, in the retraction of the head, are appressed so close as to 
seem but one lamina; but separate for the protrusion of the head with its rotating cilia. 
The hood, a decurved plate, often broad but sometimes narrow, of hyaline delicacy, is 
not retractile, but is seen when the lorica is shut up, resembling a semi-crescentic hook. 
The foot consists of three strongly marked joints bearing straight, acute, slender toes, 
often thrown wide apart, but, in some cases, so uniformly adherent that it is difficult to see 
whether they are two or one. The whole foot is often stretched behind ; but much more 
commonly it is projected forward under the belly, through the ventral gape. The presence, 
the position, and even the number of eyes, seem subject to much variation. 
Most of the known species are lacustrine in habit, but some are exclusively marine. 
It is a characteristic habit of the species of the genus, particularly of C. obtusus, to 
elevate themselves to the utmost on the toe-point as on a pivot, and then awkwardly 
tumble over, as if they had not power to maintain their balance. The Monostyle per- 
form in somewhat similar style, but though their posturings and gyrations are wild, they 
seem to have better control over them. 
