238 POTAMILLA RENIFORMIS. 



his interpretation was warranted. He noticed the peculiar curved spatulate bristles in 

 the anterior hook-rows. 



The Sabella stichophthalmus of Grube 1 (1863) does not seem to differ materially 

 from a variety of this species, though the author's figure of the first bristles must 

 have led to misinterpretations. He represents them as long, blunt hooks, and it was 

 left to Marion and Bobretsky 2 (1875) to give a more satisfactory representation and 

 description, and thus to connect it with the present form. 



Langerhans (1884) found a large variety bearing from seven to ten eyes on its 

 filaments amongst old coral at Madeira. 



Reproduction.— De St. Joseph (1894) states that the eggs are greyish. He thought 

 the Potamilla tortuosa of Webster, which makes its galleries in shells, very similar to 

 P. reniformis, and he found small examples of the latter species with the cephalic region 

 in process of reproduction. This author 3 (1906) mentions that it occurs in Oculina, and 

 he thinks it approaches the condition of a commensal like Aspidosiphon (a Grephyrean) 

 which frequents Madrepores. 



Arnold Watson's observations on regeneration were conducted on a form which he 

 thought distinct from P. reniformis, P. Torelli and Potamis, as no eye-specks occurred 

 on the branchial filaments, though just below the base of these on each side there are eye- 

 spots as in P. reniformis and other Sabellids. He counted twenty-two filaments in one 

 and twenty-four in another. The diameter of the detached plumes was 18—19 mm. 

 He called it the blushing Sabella, as its blood was red. The tube is peculiarly rugged 

 —constricted at the entrance to the burrow in the rock. An examination of this form, 

 kindly sent by Mr. Watson, shows that it appears to be a variety of Potamilla reniformis. 



A variety (AB) occurred under stones between tide-marks both in Guernsey and 

 Herm with only five pairs of anterior bristles, and. shows certain differences from both 

 Potamilla reniformis and P. Torelli. The cephalic plate of var. AB has a narrower 

 collar than in P. reniformis — a feature well marked m the small, pointed ventral lobes. 

 The edge is smooth at and near the mid-dorsal groove, then at each side is a lateral 

 flap which trends to the lamellae on the ventral surface. These lamellae are smaller than 

 in Sabella penicillus, and besides the small lamellae which project ventrally their margin 

 is incurved at the middle line. 



The body is comparatively small, about f inch in length, and the number of segments 

 is between sixty and seventy. It is rounded dorsally with the exception of the region 

 of the dorsal groove anteriorly, slightly flattened ventrally, where a median furrow runs 

 from the middle of the sixth scute backward to the tail. The anterior region is composed 

 of five bristled segments and apparently the same number of uncinigerous rows. 

 Posteriorly it tapers to a somewhat pointed tail. The branchiae seem to be comparatively 

 short, like those of Potamilla reniformis, and the pinnae of moderate length or rather 

 short, whilst the terminal filament is long, large, and is often in screw-coils, thus differing 

 essentially from those of P. reniformis, P. Torelli and P. neglecta, and resembling 



1 Archiv f. Naturges/ p. 62, pi. vi, fig. 3. 



2 'Ann. Sc. Nat./ & ser., t. ii, p. 92, pi. xi, fig. 23. 



3 Ann. Sc. nat./ 9 e ser., t. iii, p. 241. 



