POLYCERA QUADRILINEATA. 



extending from the branchiae to the tail. The branchim are situated immediately behind a 

 swelling (containing the heart) on the middle of the back : they consist of seven, or 

 occasionally nine, simply pinnate and rather tapering plumes, the largest in front : when 

 there are nine, the posterior pair are very small. Their colour is transparent white, tipped 

 with yellow or orange, and with a line of opaque white extending about one third up the stem 

 from the base. On each side of the branchial circle there is a single stout, plain, linear, 

 pointed process or lobe, which is also tipped with yellow. Foot linear, white, truncated and 

 slightly bilobed in front, and produced into short angles at the sides. 



This very pretty species is subject to great variation of colour and markings. The lines 

 of yellow tubercles, however, though varying in number, are always present. The ground 

 colour of the body, too, is invariably white, but frequently it is minutely spotted and freckled 

 with black, and a beautiful variety is marbled with dark reddish-brown and orange spots, 

 and has four rich chocolate-brown bands uniting the lateral rows of orange tubercles. 

 Another still more brilliant variety, which we dredged in Salcombe Bay in 1845, was striped 

 with alternate bands of black and bright orange-scarlet, prettily variegated with white near 

 the tentacles and branchial plumes (fig. 3). We have met with a similar variety, less, 

 brilliantly coloured, in Fowey Harbour, Cornwall. 



The appendages are also subject to variation. Sometimes an individual occurs with six 

 velar filaments, and occasionally with one or more of them bifid, but more frequently the 

 number becomes less by arrest of development, — thus we have met with specimens having 

 only one, two, or three filaments. The branchial lobes, too, are sometimes, though very 

 rarely, wanting. The naturalist must therefore be on his guard not to be deceived by these 

 sports of nature into the establishment of spurious species. Nevertheless we have met with 

 a few individuals . on the Devonshire Coast of a Polycera resembling this, but without the 

 tubercles, and differing in so many other points that we are much inclined to consider it 

 distinct. 



There is some little difference in form between the generality of south country specimens 

 and those got on the Northumberland Coast. In the former the tentacles and branchial 

 plumes are more slender towards the apex than in the northern form, but we think they are 

 probably only varieties. 



The Polycera typica of Thompson differs from P. quadrilineata in nothing but the size of 

 the branchial lobes, which in that species are large and inflated. We had at first thought that 

 this might prove a good distinction, but have since found that these, as well as the other parts 

 of the body of these little creatures, are apt to become inflated when they are in a sickly state, 

 and that specimens of the ordinary kind have occasionally had the branchial lobes thus 

 inflated after coming into our possession. We are compelled, therefore, to consider the 

 P. typica only an accidental state of the present species. Polycera quadrilineata is widely 

 diffused through the European seas ; extending from Norway to the Mediterranean, whence 

 specimens have been sent us by M. Verany. Our list of localities will show that its 

 distribution round the British coast is very extensive. It inhabits the littoral and 

 laminarian zones, and may sometimes be found congregated in considerable numbers on small 

 sea-weeds, in pools among the rocks near low-water mark, especially in the summer months, 

 when it is spawning. The spawn forms a small, broadish, white strap, attached by one of 

 its edges to sea-weed, and arranged in a single imperfect coil. The eggs are very small and 

 numerous. 



