238 GIGLIOLI, ON THE GENUS CALLIDINA. 
ised by the total absence of eye-spots, the smallness of their 
trochal disc, and the vivacity of their movements. 
I intend to describe briefly the three known species, and 
to dwell more minutely on the fourth, which I discovered 
last winter, and believe to be new. Before commencing I feel 
it my duty to express my sincere thanks to Mr. Gosse, who 
contributed not a little to lessen the difficulties 1 encountered 
in working out the affinities of the last-mentioned species by 
the generous loan of his valuable drawings and MS. observa- 
tions. I shall give the species in the order they were dis- 
covered and described. 
Callidina elegans,* Ehr—Body spindle-shaped; trochal 
disc small. The digestive canal, which is figured filled with 
a dark-blue colouring matter, is a narrow, wavy tube, dilating 
distally, and not occupying the whole breadth of the granular 
mass which surrounds it; the mastax is very indistinctly 
figured, but in the text Ehrenberg describes it as being pro- 
vided with many delicate teeth. The total length of the 
animal is *37. It was first observed in a pond near Berlin. 
Callidina constricta,t Dujard.—This species was first dis- 
covered at Toulouse, in 1840. Its mastax, according to 
Dujardin, presents “une rangée de petites dents paralléles.” 
The trochal dise is much constricted, whence its name. 
Truly the characters of this species are very similar to 
those of the preceding one, the only difference being in the 
length, which here is ‘5. 
Callidina bidens,t. Gosse.—This species was first observed 
by Mr. Gosse, in London, in 1849. He describes it as being 
spindle-shaped, =!;th of an inch in length, and possessing 
only two teeth in the mastax. Mr. Gosse expresses a doubt 
whether this may not be C. elegans of Ehrenberg, but the 
number of teeth is quite different. It is, however, more than 
likely that Dujardin’s and Ehrenberg’s species are identical. 
None of the above-described species are parasites. 
Callidina parasitica, mihi.—This species may or may not 
be distinct from the preceding one; I firmly believe it is. It 
certainly differs from C. bidens in its parasitism; moreover, 
many other minor differences exist, in the size and shape of 
different organs; but as it is no easy matter in these days to 
define the true characters required to constitute a species, I 
shall leave it to future investigators to decide. 
Last winter, while engaged in examining the contents of 
* Threnberg, ‘Infusionthierchen,’ p. 482, pl. lx, fig. 1. 
+ F. Dujardin, ‘ Infusoires,’ p. 658, pl. 17, fig. 3. 
+ P. H. Gosse, ‘Ann. and Mag. of Nat. Hist.,’ vol. viii, 2nd series, 1851, 
p. 202. 
