POTAMILLA TOEELLI. 239 



apparently those of Spirobranehus. Moreover, there are no ocelli on the filaments, and 

 none on the first segment or on the tail. 



The first region of the body has only five pairs of setigerons processes. Each 

 bears a tuft of comparatively short bristles, the tips of which, unfortunately, had for the 

 most part disappeared, probably from their brittle nature as well as from rough usage. 

 Those which are perfect have shafts which slightly dilate from the base to rather beyond 

 the middle, then diminish at the neck and swell out at the origin of the wings, tapering 

 thereafter to a somewhat long attenuate extremity. At the upper edge of the fascicle 

 are the longer and more slender forms, the shafts of the others being thicker. Spatulate 

 forms also occur as in the type. The anterior hooks (Plate CXXVIII, fig. 1 b) form 

 a single row, and present a sharp main fang, the rest of the anterior face of the 

 crown above it (about half the extent) being finely serrated in lateral view, as usual in 

 such hooks. When the crown is examined from the front this region is densely spinous. 

 The posterior outline is more or less straight below the forward bend at the crown, 

 whilst the anterior is also straight immediately below the main fang, curved forward over 

 the rounded prow. The projection of the base posteriorly is narrow, but somewhat 

 shorter than in Potamilla reniformis. Each is accompanied by a short, broad, cuspidate 

 or penniform bristle. The hooks behind the anterior region in the fragmentary example 

 do not materially differ, though the neck is longer, the base somewhat shorter and their 

 size less (Plate CXXVIII, fig. 1 c). 



The small number of the anterior segments, so unusual in the group, though this 

 number has been found in P. Torelli, raises the question as to its relationship to the 

 latter, from which it differs in the terminal processes of the branchiae and in the narrower 

 web in the anterior bristles, but further investigations may clear up the divergences. 

 Like many Sabellids it is acid to litmus paper. In the example from St. Peter Port, 

 Guernsey, the tube is composed of a translucent, horny secretion somewhat like that of 

 Potamilla reniformis. Some examples have nearly ripe ova (July and August). 



Amongst the forms which show similar hooks anteriorly are the various species of 

 Eudistylia, Bush, Schizobranchia, Bush, Parasabella, Bush, Pseudopotamilla, Leidy, and it is 

 possible that further examination may lead to the diminution both of genera and species. 



Potamilla Torelli, Malmgren, 1865. Plate CXIV, fig. 3— body ; Plate CXX, figs. 7 and 

 7 a — branchiae ; Plate CXXVIII, figs. 3 — 3 d— bristles and hooks. 



Specific Characters. — Cephalic plate and collar as in P. reniformis, the collar having 

 a narrow slit dorsally, then extends to the ventral lamellae, which are usually reflected in 

 protrusion and separated from each other by a deep V-shaped notch. Branchial filaments 

 of moderate length and pale, eight to sixteen in number, and each ends in a short, thick, 

 distal process. Pinnae of average length, the distal ten or twelve gradually diminishing, 

 to end in a papilla-like rudiment at the base of the terminal process. Oral fold passes 

 from each side of the ventral lamella upward, and its end fuses with the middle of each 

 branchial fan. A considerable portion of the dorsal edge of the base of the branchiae 

 bordered by a mobile flap, the ventral edge adjoining the mouth. The branchiae are 



