COLURUm 101 



Family XVI. COLURIDjE. 



[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 Metopidia 

 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 distinction 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 Metopidice, for instance, is so very uncertain and indetermin- 

 able, that I incline to agree with Dujardin in rejecting some of Ehrenberg's genera. The 

 distinction between Lepadella, Metopidm, and Squamella, is more than doubtful ; while 

 in Metopidia and Colurus, 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 subglobose, 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-circular 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, acmte, 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 subjeet 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 MonostylcB per- 

 form in somewhat similar style, but though their posturings and gyrations are wild, they 

 seem to have better control over them. 



