POTAMILLA RENIFORMIS. 235 



in number on each side and comparatively short, whilst the pinnae are long. Each 

 filament has the transversely barred or camerated chordoid axis, and tapers to a short 

 filiform tip, which, however, is usually enveloped by the long pinnae or is in screw-like 

 coils. The pinnae have the translucent axis as in S. penicillus with long joints, and are 

 richly ciliated. In life the branchiae are of a pale green marked with white touches, so 

 that they form a whitish ring around the collar, within which they are attached. The 

 pinnae are variegated with pale greenish and white and show vermiform movements when 

 cast off. In some the branchiae are of a pale buff hue with a little yellow at the tips of 

 the filaments. In contraction they are generally of a dull stone colour. Leuckart's 

 examples had whitish branchiae with brownish touches, and De St. Joseph describes his 

 examples as vinous-brown. Sars states that his specimens had yellowish-white branchiae 

 with four or five orange bands. Just above the whitish ring at the base most of the 

 filaments have externally two boldly marked and elevated brown or reddish-brown 

 ocular specks separated by an interval from each other. De St. Joseph states that in 

 his specimens each contained about thirty ovoid " crystalling " in a mass of brownish 

 pigment. Moreover, the eyes of those from the Mediterranean are more numerous 

 than those from the north, whilst ^ Marion considered that those from deep water had 

 fewer eyes than the littoral forms. They are absent in a few of the filaments. The 

 longest filaments are dorsal, those at the ventral edge being considerably shorter and 

 slightly reflexed. The ocular pigment in some fades in spirit. The tentacle is com- 

 paratively short, but its membranous web on each side appears to agree with that in 

 Sabella penicillus. 



The branchiae of this species are more translucent and feathery than those of 

 P. Torelli, the pinnae more delicate and longer, and the coloration of the two forms 

 diverges. The terminal processes of the branchiae are short, whereas those of P. Torelli 

 are long and opaque whitish. In an example of P. reniformis the bases of the branchiae 

 were reddish brown with a pale band, whilst the rest of the filaments were pale. In 

 P. Torelli the branchiae are boldly blotched with brownish red and white and the long 

 terminal filament is opaque white. The ocelli in P. reniformis are also diagnostic, and in 

 some they are confined to the base of the filament. The white specks on the body of 

 P. Torelli also differentiate. 



The body is comparatively small, about three-quarters of an inch in length, and has 

 from sixty to a hundred segments. It is rounded dorsally, slightly flattened ventrally, and 

 marked by a groove, which at the tenth segment bends from the side inward to the middle 

 line and divides all the scutes which follow into two. The ten scutes in front of these are 

 split transversely. The ventral scutes are conspicuous by their whitish or pinkish colour, 

 and are even visible through certain parts of the tube. Anteriorly the brownish dorsum 

 is marked with dark brown pigment at the bases of eleven setigerous processes, the 

 succeeding region of the dorsum being reddish brown. The surface is paler in the median 

 line dorsally and ventrally. The body is slightly tapered posteriorly, and ends in a 

 papillose anus, three papillae being distinct, and the colour of the tip is orange rather 

 than brown. 



An interesting variety was procured by Arnold Watson at Llanfairfechan, Wales, in 

 which the anterior region consisted of no less than twenty-six segments, the first eight 



