212 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



red. Older specimens, especially if taken from sand in 

 which the amount of organic matter is considerable, are 

 nearly black in colour and their gills, which are also 

 pigmented, are better developed than in young specimens. 

 The second variety of A. marina is found in the upper 

 part of the Laminarian zone, and can only be readily 

 obtained at very low tides. It breeds in the spring, from 

 the beginning of March onwards. t When fully grown 

 it is one of the largest Polychsets of our shores, measuring 

 as much as 400 mm. (16 inches) in length and nearly three 

 inches in girth at its widest point. It is dark brown or 

 almost black in colour. Its burrow, in which the worm 

 is found head downwards, appears to be simply vertical 

 and not U-shaped. The most distinctive character of this 

 variety is, however, the gill, which is a highly developed 

 pinnate structure (fig. 19) consisting of about twelve stems 

 united by a connecting membrane at their bases and 

 bearing ten or more branches on each side of the axis. 

 The Laminarian differs from the littoral form also in the 

 sub-division of the interval between the second and third 

 cliBetigerous annuli ; in the former this region is divided 

 into two rings and in the latter into three (see figs. 1 and 

 2). There do not appear to be any other structural points 

 of difference. The Laminarian variety is abundant on 

 certain parts of the Lancashire coast, e.g., near Blackpool, 

 where specimens are obtainable at low tides on digging to 

 a depth of about three feet in the sand near extreme low- 

 water mark. I have recently found four specimens* of 

 this variety in a collection of Arenicola from the sand 

 between Portobello and Musselburgh on the Firth of 

 Forth. The Laminarian variety has also been found in 



t See footnote (f) on p. 211. 



* The gills of two of these were not as obviously pinnate as those 

 of the Laminarian forms of the Lancashire coast. 



