PBIONOSPIO. 213 



1909. Polydora hoplura, Mcintosh. Ann. Nat. Hist., ser. 8, vol. iii, p. 173. 



» v >> Lo Bianco. Mitt. Zool. Stat. Neapel, Bd. xix, p. 584. 



1910. „ „ Bather. Geo]. Mag., Dec. V, vol. vii, p. 114. 



1911. „ „ Journ. M. B. A., vol. vii, p. 228. 



1914. „ „ Southern. Proc. Roy. Irish Acad., vol. xxxi, no. 47, p. 103. 



Habitat. — Between tide-marks, Lochmaddy, North Uist, and amongst Polydora ciliata 

 at the Castle Rocks, St. Andrews. Plymouth (Allen). Clare Island district (Southern). 



Abroad it occurs on the Shores of France, perforating oysters (De St. Joseph, Mesnil). 

 Mediterranean (Claparede, who discovered it in the tests of Balani at Naples). Marseilles 

 (Marion and Bobretzky). 



The head of this form does not differ much from that of P. ciliata, with which it 

 associates at St. Andrews, except in the absence of the dark pigment on the snout in the 

 preparations, and, perhaps, its slightly smaller proportions. The prostomial prow has a 

 median notch and two rounded lateral regions. 



The arrangement and shape of the lamellae and bristles of the first four bristled 

 segments are also like those of P. ciliata. 



The fifth segment bears hook-like bristles which are distinguished at first sight from 

 those of P. ciliata by their parallel arrangement in the group in situ, especially at the 

 tips, a feature due to their more uniform diameter, by their peculiarly curved and by no 

 means sharp tips, and by the position and size of the lateral spur at the neck (Plate CVI, 

 figs. 6 a and 6 b). 



The branchiae commence on the seventh segment, as also do the winged hooks 

 (Plate CVI, fig. 6 c), which show rather a long, sharp main fang, coming off nearly at a 

 right angle with a single spur above. 



The feature most diagnostic of this species was unfortunately absent in the imperfect 

 specimen, viz. the presence of the hook-like bristles (Plate CI, fig. 10) in the last fifteen 

 segments. From Claparede's figure these apparently occupied the ventral division to the 

 exclusion of the winged hooks. An example sent by Mr. Southern enabled the figure to 

 be made. 



Reproduction. — At Naples the period of sexual maturity, according to Lo Bianco 

 (1909), is from June to November. 



Claparede (1868) describes a peculiar series of vascular loops or lozenge-like figures 

 formed in the region occupied by the sexual elements on the ventral surface, and a 

 glomerulus at the base of the branchiae. The first segmental organs occur in the ninth 

 segment. 



Genus CIIL— Prionospio, 1 Malmgren, 1867. 



Cephalic region short, truncate in front, a little elevated and subrectangular in out- 

 line. Tentacles not conspicuous. Eyes present or absent. Body elongate, sublinear, a 

 little attenuated posteriorly. Setigerous tubercles with flattened lamellae which are large 

 in the first four segments. Branchiae four pairs in the anterior segments, dorsally adnate, 

 the first and fourth having a long pinnate process, that of the second and third being much 

 shorter and filiform. Bristles in the anterior segments capillary in both divisions, in the 



1 n£iwu et ^irtiior]. 



