232 POTAMILLA RENIFORMIS. 



A small variety (it may be a different form) was found by Roule 1 at a depth of 

 950 metres. 



Genus CLXII. — Potamilla,- Malmgren, 1865. 



Dorsal collar bilobed, the rim passing at each side ventrally to a notch, and the ends 

 curve forward. Body as in Sabella. Ventral sulcus conspicuous, not continued dorsally 

 in the anterior region. Setigerous processes commencing at the collar- segment. Bristles 

 of two kinds, the longer having tapered tips, the shorter sub-spatulate with unequal 

 wings. Hook-rows begin on the second segment, and the hooks are of two kinds, the 

 one avicular, the other with a short shaft and spatulate tip. Only the avicular hooks 

 posteriorly. Branchias forming a half -fan on each side connected at the base; no dorsal 

 processes; occasionally eye-specks. Two short, compressed, tapering tentacles. Tube of 

 a tough secretion with sand-grains and other foreign particles. 



1. Potamilla keniformis, Leuclcart, 1849. Plate CXIV, figs. 2 — 2b — body; Plate 

 CXXVIII, figs. 2— 2f— bristles and hooks. Compare with Plates CXXVII, fig. 7, 

 and CXXVIII, fig. 1— varieties. 



Specific Characters. — Cephalic plate with a bilobed white collar dorsally ; then the rim 

 passes on each side to a ventral notch separating the ventral ends, which curve forward. 

 The truncated cephalic surface has a projecting transverse fold at the upper end of the 

 ventral incurvation, and two folds meet above it so as to make a triradiate aperture. 

 Branchiae comparatively short, about ten in each fan, the tips short, slender and filiform. 

 Most of the filaments have two conspicuous and elevated brown or reddish-brown or dark 

 violet ocular specks separated by an interval from each other. 2 Tentacles short, but the 

 membranous web is like that of S. pe?iicillus. Body comparatively small, about f inch, 

 and having 60 — 100 segments, but the southern examples are larger, De St. Joseph giving 

 12 cm. and 290 to 300 segments, of which 9 — 12 or more are anterior; rounded dorsally, 

 flattened ventrally, where a groove at the tenth segment bends inward to the mid- 

 ventral line and continues to the tail, which is tapered and ends in an anus with three 

 papilla? and several violet pigment-specks. Anterior region of 12 segments (11 setigerous 

 processes). Anterior setigerous processes bear two kinds of bristles, about three longer 

 dorsal having straight shafts and tips with moderate wings bent backward, and a double 

 series of spatulate forms with a short process at the tip. The posterior bristles have 

 narrow wings and long tips. Anterior hooks with a finely serrated crown above the 

 main fang, a ridge below the crown, a somewhat long, longitudinally striated neck and a 

 long base. Bach hook is accompanied by a short thick bristle with a spatulate tip. The 

 posterior hooks are smaller, have a longer neck, a more pointed crown, and a shorter 

 base, with a tendency to slope downward. Tube of a tough horny secretion of an olive 



1 Camp. " Caudan," p. 164. 



2 Cams, ( Fauna Medit./ gives five to eight. 



