COLURIDA. 109 
M. practga, Ehrenberg. 
Squamella bractea . . 5 Ehrenberg, Die Infus. p. 480, Taf. lix. fig. 16. 
(SP. CH. Lorica oval, much depressed, its front deeply excavated especially on the 
pectoral side; dorsal plate ending behind in two minute projections ; ventral deeply 
excavate ; eyes four. 
The differences perceptible between this and lepadella are exceedingly small; the 
four minute eyes, set in square, are very rarely discerned ; but I have seen them. One 
deposited an ephippial egg, clothed with very long spines, while under my observation. 
PEGs 
Length. Of lorica, 5}, inch. Habitat. Pools and infusions ; common (P.H.G.). 

Genus MONURA, Ehrenberg. 
(GEN. CH. As Colurus, but the toe is a simple style. 
It is mainly in deference to the great Prussian zoologist, that I retain the generic 
distinction between this and the preceding group. With the recollection that in C. leptus 
I can discern no trace of a medial depression in the toe, that in C. amblytelus there is 
the depression, which I have never seen separated, that in C. caudatus there is the de- 
pression apparently as inseparable, which, yet, on occasion, palpably opens and expands ; 
to build a genus exclusively on this condition of the toe is most precarious.—P.H.G.] 
M. coturus, Ehrenberg. 
(Pl. XXVI. fig. 7.) 
Monura colurus 6 . o : Ehrenberg, Die Infus. 1838, p. 474, Taf. lix. fig. 4. 
[SP. CH. Lorica ovate, much compressed, highest at the front, with the hind ends 
rounded ; eyes two, approximate. Marine. 
Viewed vertically this animal has the form of a mussel, gaping widely all along the 
venter and around each extremity, with no sensible change of outline for the emission 
of the foot, and hinged only along the middle of the dorsum. In a lateral view the 
lorica forms the half of a very long ellipse, flattened ventrally, obtuse behind, thence 
gradually rising till it is highest at the front, whence it descends in a bold curve to 
rejoin the belly side. Thus the outline is markedly different from that which is charac- 
teristic of Colurus, though the difference depends on minute peculiarities. 
The round anteriors of the valves are, often and long, firmly appressed (fig. 7a), the 
whole head and viscera being far withdrawn, and a wide hyaline space left, within 
whose edge a very delicate corrugation marks the line of mutual contact. At intervals 
the valves part, and a head is protruded, armed with long and coarse cilia, and oyer- 
arched by a conspicuous frontal hood. This has the unusual appearance of a wide veil 
of exceeding tenuity, strengthened by an acute taper hook of chitine running through its 
medial line. Under the base of this organ are seen two brilliant crimson eyes, 
moderately near each other. Slight indications of a manducatory apparatus are seen, 
and occasionally the globose form of the mastax ; but all so evanescent as to defy defi- 
nition. A large sacculate stomach, divided by constriction from a still ampler intestine ; 
an ovary and a small contractile vesicle, with the cloaca at the dorsal base of the foot, 
are all normal. The foot itself is prominent, moderately thick, of three long, well- 
marked joints ; the toe, a single, long, acute style, thick at base, and suddenly diminish- 
ing in its dorsal outline, has the remarkable peculiarity of being as flexible and elastic 
as whalebone. The extruded foot and toe are two-thirds as long as the lorica. 
I first met with this species, congregating in great numbers around my marine 
