4 THE KOTIFEBA. 



SP. CH. Spines twelve broad blades with serrate edges. 



When gliding along under the action of its ciliary wreath Polyarthra seems to have 

 a triangular outline ; for the body, though itself truncated both in front and rear, 

 carries four clusters of serrated blades fastened to the shoulders ; and these trail behind 

 so as nearly to meet in a point, at some distance from the animal's body. Every now 

 and then the blades are jerked vigorously forward, and the creature is tossed out of its 

 path, several times its own length. The trunk is partially loricated. There is a kind 

 of chitinous shield running down each side of the body, pointed at its hinder end, and 

 bent at the sides so as to encroach a little on the tough dorsal and membranous ventral 

 surfaces. The edge of the dorsal lorica (if it may be so termed) is plainly visible run- 

 ning across from one cluster of blades to the other. A pair of powerful striated muscles, 

 forming a letter V, is fastened to the lower pointed end of the shield, and to the inner 

 surface of the soft tissues, to which, at the upper end on each side, six of the blades are 

 attached. The contraction of these V-shaped muscles drags the soft tissues sharply 

 down over the hard edge of the shield, and makes the blades fly out with great swift- 

 ness. The blades are curiously like a bird's feather in general outline (fig. 5d), having 

 a midrib (fig. Be] and being distinctly serrated on both edges. The corona is slightly 

 convex and bears, towards the dorsal surface, two prominences like those of Synchceta 

 pectinata, each carrying a brush of styles. There are also two long styles facing these, 

 and springing from the corona towards the ventral surface. Mr. Gosse has, moreover, 

 noticed, besides these tactile organs, a small occipital pimple armed with bristles. The 

 very large mastax points obliquely downward to the ventral surface. Both it, and its 

 trophi, closely resemble those of Synchcsta pectinata. The contractile vesicle can be easily 

 seen, but neither lateral canal nor vibratile tags have been recorded. Nothing else in 

 its internal structure requires notice. 1 The animal carries the great female egg singly, 

 and transversely, between the points of the two side shields ; but the small male eggs in 

 clusters of half-a-dozen or more at a time (fig. 5b). The male was discovered by Mr. 

 Gosse in 1850, and described and figured by him in the " Phil. Trans." for 1856. [Its 

 length is only -^ inch. The head is very large (fig. 5/t) and the body tapers quickly to 

 the posterior part, but both extremities are truncate. The front bears two warts between 

 which the rotatory cilia are placed, but the cilia are longer (perhaps setae) on the warts. 

 The hinder part is bifid, the smaller division being the caudal extremity or toe-less foot, 

 and the latter a protrusile truncate penis ciliated at the tip. No internal organization 

 was discoverable. P.H.G.] Dr. Plate's figure (loc. cit.} shows the sperm-sac. 

 Length. Female's body, ^^ inch. Habitat. Pools and ponds : common. 



Genus PTEROESSA, Gosse. 



[GEN. CIT. Lorica entire, save for a large oval opening behind; beset with arti- 

 culate pinnate, styles, and simple setae : foot wanting. 



P. SURDA, Gosse, sp. nov. 

 (PL XIII. fig. 9.) 



RP. CH. The only known species. Horny yellow ; pinnae twenty -four, in six longi- 

 tudinal roics. 



The form of this remarkable species is that of an ancient amphora ; a long oval 

 tapering to an obtuse point, with no foot, forming a constricted neck, in front, and thence 



1 An observation of Mr. Gosse's leads him to think that the rectum is turned far forward as in the 



Eh:~ota ; and that it IB capable of considerable protrusion, though ordinarily invisible. 



