COLURIDA. 107 
This charming species, though in technical characters very similar to the preceding, 
is yet readily distinguished when once it is known. It is very much rarer, averages nearly 
twice its size, while its outline, in retraction, far more nearly approaches a circle. This, 
with its crystalline brilliance, recalls the lovely Pterodine, of which it is no unworthy 
rival; and its resemblance to them is much augmented by a delicate line of corrugations, 
which run round just within the margin, like the ‘‘millmg” withm a shilling. It 
was this feature that suggested the specific name, and no allusion to the adjective solidus. 
The arch of the lorica is much lower than in lepadella, especially towards the edge, 
while down the middle there runs a very low, rounded ridge. The fore and hind exca- 
vations are nearly as in lepadella. Besides the frontal hood, there is another clear disk 
which appears to protect the rotating cilia, and a transparent bulb is placed on each side 
of this, within each of which is seen a minute red eye, so that these organs are widely 
separated. 
Some curious facts connected with digestion were illustrated by mixing a little car- 
mine with the water. Particles were readily imbibed, and soon appeared as a red cloud 
in the fore part of the stomach. Presently this pellet passed into the upbent viscus at 
tlie bottom, which I supposed the intestine ; and a second pellet, swallowed at the same 
instant, took the vacated place. After an hour, the whole alimentary canal had assumed 
the appearance of fig. 11f, the supposed intestine being only a lobe or pocket of the 
stomach. The pellet No. 1 now moved rapidly down to the cloacal extremity of the 
twofold viscus, but, instead of being discharged, it swiftly passed up (as between the 
dotted lines) to its first position at the base of the stomach; then returned to the 
cloacal end, and quickly again mounted ; repeating these movements several times, till 
at length it coalesced with the second pellet. All the while the whole interiors of both 
chambers were full of an incessant quivering from the action of epithelial cilia. From 
all this, it really seems as if something analogous to rumination occurred in these minute 
creatures. The gastric glands and the lateral canals are very abnormal ; and the con- 
tractile vesicle is sometimes ample, sometimes totally wanting.—P.H.G.] 
Length, ;!, inch. Habitat. Walthamstow; Leamington; Birmingham; Woolston ; 
Dundee (P.H.G.). 
M. acuminata, Ehrenberg. 
(Pl. XXV. fig. 9.) 
Metopidia acuminata 6 : Ehrenberg, Die Infus. p. 477, Taf. lix. fig. 11. 
[SP. CH. Lorica ovate, ending behind in an acute point ; occipitally deeply notched 
between projecting spines ; the edges very thin. 
Besides the above peculiarities there is little to mark this obscure little species, which 
yet is amply distinct. When seen sidewise it has much likeness to a Colwrus, save that 
its form is flatter ; and the decurved frontal hood is more conspicuous. It is an eager 
and persevering feeder, raking with its hood-edge among the floccose,—P.H.G.] 
Length. Of lorica, 3, to 31, inch. Habitat. North London; Leamington; Sand- 
hurst (P.H.G.); very scarce. 
M. oxysTERNUM, Gosse. 
(Pl. XXV. fig. 8.) 
Metopidia oxysternon 6 ; 3 Gosse, Ann. Nat. Hist. 2 Ser. vol. viii. 1851, p. 201. 
[SP. CH. Lorica an ovate bor of tesselated surface ; with a thin ridge running 
down the dorsum ; venter with a similar medial ridge terminating abruptly in mid-lenath. 
This is a very curious form. It is a depressed rhomboid-oval, with a rather high and 
thin arched ridge running down the back from the bottom of a deep frontal sinus. The 
ventral surface is also ridged as far as the mid-length, where the ridge ends, like the 
sternum of a bird. Then the surface is deeply excavated, and again projects, forming a 
prominent sheath for the emission of the foot. The whole lorica is cut into facets, as 
