ANNELIDA POLYCHAETA. 41 



Society of Nat. History, Vol. V, 1856, p. 114; A. antil- 

 lensis Lütken. loc. cit. 



Among the Arenicola-STpecimens of Naples there are two 

 individuals , agreeing with A. marina in feature and size 

 of the body , but plainly distinguished from it by several 

 characters. The number of setigerous segments is only 17, 

 of which the posterior 11 are provided with branchiae. 

 The first branchiae, situated on the 7th segment, as in 

 A. marina , are less developed than the following. The 

 branchiae consist of about 12 branchial leafs, situated next 

 to each other in the same plane , but scarcely connected 

 by a membrane at their base ; each branchial leaf has a 

 long middle axis and a great number (to 20) of short, 

 branched filaments on each side, resembling a feather. 

 The bristles of the dorsal fascicles have about the same 

 length as those of A. marina , but they are more nume- 

 rous and darker coloured; they are arranged in two dis- 

 tinct transverse rows , the bristles of the posterior row 

 being twice as long as those of the anterior one. The brist- 

 les are more hairy as those of A. marina ; the transver- 

 sely striated membrane along the distal portion of the 

 bristles in this species , is substituted here by a broad row 

 of distinct hairs , and also along the other side of the 

 bristle short hairs are to be found (fig. 9). The anterior 

 two setigerous segments seem to want the ventral fasci- 

 cles, at least they are not visible externally. The ventral 

 bristles are slender , with a more or less curved tip ; at a 

 short distance beneath the tip they are a little enlarged 

 and furnished at the convex side with a great number of 

 faint serrations (figs. 7 and 8). 



The proboscis is covered over its whole surface with 

 large rounded , triangular papillae. 



Length of the largest specimen 230 m.m. ; length of its 

 caudal region 85 m.m. 



A. cristata , described by Stimpson from the shore of 

 Maurice-Island (South Carolina), seems to agree in its main 

 . characters with our specimens ; therefore , though Stimpson 



Notes from the Leyclen Museum, Vol. XI. 



