TRIARTHRADA. fi 
intervals, and unite with the broad band round the neck in driving out the retracted 
head, and restoring the spines to their usual position. 
Length. Without the spines, +}; inch. Habitat. Fresh-water ponds and ditches : 
common. 
T. mysracina, Hhrenberg. 
(Pl. XIII. fig. 8.) 
Triarthra mystacina : : Ehrenberg, Die Infus. 1838, p. 447, Taf. ly. fig. 8. 
[SP. CH. Body oval; buccal orifice taking the form of a beak projecting from the 
face ; spines not twice the length of the body ; eyes approximate ; esophagus invisible. 
In July 1849, from the ditch at Dalston Causeway, near London, I took several of 
the Whiskered Three-beard. ‘The moderate length of the leaping spines, the approxi- 
mate eyes, and the absence of any manifest cesophagus—the stomach coming into contact 
with the mastax—marked the species as Ehrenberg’s mystacina. The absence of the 
esophagus is doubtless only apparent, this duct, as is the case with Polyarthra (see 
Pl. XIII. 5c) and many other Rotifera, issuing from behind the mastax, near its summit. 
One adult had an egg attached to the hind extremity, which somewhat retarded its 
motions, as compared with those of its fellows. After a while the spontaneous move- 
ment of the embryo became more and more vigorous, and the ciliary rotation energetic ; 
and a clear globule, as of air, was seen within, while yet the egg remained adherent. 
The front is formed of a ring of six or seven sub-globose masses, in mutual contact, 
each of which is crowned by a cluster of divergent cilia. The chin descends in a promi- 
nent hook, like a parrot’s beak, which appears stiff, and projects between the bases of 
the two pectoral spines. The two eyes are nearly frontal, small, bright red, and 
approximate. The mastax appears formed on the plan seen in the Bdelloida. The 
stomach is large and saccate, and is supplemented by a distinct intestine. The animals 
are very subject to be infested by two species of Colaciwm, which are seen in fig. 8. 
They cling to its spines as well as its trunk, and appear to give it uneasiness. I have 
counted sixty-five of these parasites on one individual, and nearly fifty on another. 
The animal seems to have no power of affixing itself, or of resting. It swims con- 
stantly ; interrupted only by its spasmodic jerks or leaps, performed by the sudden 
throwing out of the elastic spines, chiefly, I think, the pectoral pair. These are 
articulated to shelly knobs, which imply a solidifying of the integument around their 
bases, to supply the necessary resistance. In the act of springing, these two are often 
shot forward so forcibly as to be projected in front, reminding us of the anal bristles in 
Podura. This is done with a rapidity that the eye cannot follow; and this, through so 
dense a fluid as water, requires the exertion of great muscular power.—P.H.G.| 
Length. To tips of sete, ,, inch. Habitat. Around London: ditches and orna- 
mental waters (P.H.G.). 
T. BREVISETA, Gosse. 
Triarthra breviseta . a 8 . Gosse, Ann. Nat. Hist. 2 Ser. vol. viii. 1851, p. 200. 
[SP. CH. Body cylindrical; breast projecting, but not beaked ; spines not onc- 
fourth as long as the body. 
This species is more regularly cylindrical than the others; it is diminished toward 
the front, which is truncate; the hinder end is ventricose, and extends much beyond the 
base of its spine; the belly is deeply sulcate, with thick collops of the skin between ; 
the breast forms a great rounded projection, but not a beak. Just beneath this is a 
constriction, where the very short spines are set, each not more than half the body’s 
width in length, very slender. The whole head can be retracted as far as this, by which 
involution of the skin the spines point straight forward, reverting to their normal direc- 
