SABELLA B.C. 243 



occurrence of scissiparity in this species in so far as they found in the tubes adults with 

 regenerating posterior extremities, whilst beside them were smaller forms of twenty-eight 

 to thirty-five segments, corresponding to the original tails, and with developing branchiae. 

 They concluded, therefore, that the species was scissiparous. 



Potamilla incerta, Langerhans, which Dr. Allen procured by the dredge on Yealm 

 ground, Plymouth, seems to be the young of Potamilla Torelli, and in this Prof. Fauvel 

 agrees. Indeed, it is difficult to find satisfactory distinctions between Potamilla reniformis 

 and P. Torelli, for the absence of ocular points on the branchial filaments may not be of 

 capital importance. P. incerta has five thoracic segments. 



3. Sabella B.C. Plate CXX, fig. 6— ventral view of anterior region; Plate CXXVIII, 



figs. 1 — 1 c — bristles and hooks. 



Specific Characters.— After removal of the branchiae the cephalic region presents no 

 deep dorsal fissure. Collar commences as a narrow process on each side of the dorsal 

 furrow, slopes obliquely forward and outward and incurves laterally and ventrally into 

 a deep though thin lamella, which attains its maximum in the mid-ventral line, where it is 

 separated from its fellow by a fissure. Branchiae reddish brown in spirit, about eleven 

 filaments on each side, connected only at the base ; pinnae short ; a terminal strap-shaped 

 process. Body distinctly segmented ; segments fifty-six or more. Ventral surface with 

 scutes throughout. Five or six bristled segments anteriorly, the hook-rows being one less 

 in each case. Bristles with straight shafts, finely tapered tips and narrow wings, dorsally 

 and ventrally with spatulate tips, the outline of the wings being more or less elliptical. 

 Posteriorly the bristles form a tulip-like fascicle. Anterior hooks with a main fang and 

 a series of serrations above it, a boldly convex prow, and an oblique, tapered base. A 

 series of modified (beak-like) bristles accompany them. Posteriorly the hooks are 

 smaller, their necks longer and the bases more oblique. 



Tubes of secretion with a few grains of sand attached. 



It appears to be a variety of Potamilla Torelli, though presenting certain features of 

 its own. 



Synonym. 

 1916. Sabella B.C., Mcintosh. Ann. Nat. Hist., ser. 8, vol. xvi, p. 13. 



Habitat. — Procured at Berehaven in numbers by the Eoyal Irish Academy's Expedi- 

 tion, 1886. When the branchiae are absent the cephalic region presents no deep fissure as 

 in ordinary Sabellids, but the slight dorsal furrow ends in a solid mass, which, with an 

 incurvation in the middle, passes from side to side, and then bounds the region laterally 

 to the ventral surface. This rim forms a projecting base to the branchiae. The collar 

 commences as a narrow process on each side of the dorsal furrow, slopes obliquely 

 forward and outward, and inclines laterally and ventrally into a deep though thin lamella, 

 which attains its maximum in the mid- ventral line, where it is separated from its fellow 

 by a fissure. The branchiae preserve much of their reddish-brown coloration in spirit, 

 and they are of considerable length. The pigment is arranged on the pinnae so as to 



