112 



Arenicolidae 



of which is either simple or divides dichotomously once or twice, the 

 finger- or thumb-shaped gill-filaments forming clusters at the end of 

 each axis ; the median lobe of the prostomium is small, the lateral 

 ones are well developed but not markedly dilated and not folded at 

 their anterior ends ; neuropodia are clearly visible in each chaetiferous 

 segment, those of the posterior branchial segments are long dorso- 

 ventrally and almost reach the mid-ventral line; six pairs of 

 nephridia, which open on the fourth to the ninth segments; one 

 pair of conical oesophageal glands ; a pair of small septal pouches ; 

 a pair of statocysts, opening to the exterior, and each containing 



numerous statolilhs composed of sand 



^flHKkw .--PR. 



grains. 



HISTORICAL ACCOUNT. A few speci- 

 mens of Arcnicola five picked up on the 

 beach (12th Sept., 1882) at Cape Smyth, 

 Alaska, after a fresh westerly gale, and 

 two mutilated ones taken from the gullet 

 of an eider duck provided the material 

 on which this species was based. Murdoch 

 gave little information concerning his new 

 species ; he remarked that the worms under 

 Fig. 46. A. giaciaii*. Anterior end, observation were closely allied to A. 



dorsal aspect ; PR. Prostomium ; -1^11111 i i 



N.GK. Nuchal groove, the posterior manna, but they had only eleven branch- 

 lip of which is slightly everted. ./> TT i -r, j -11 



Both the iirst notopodia (NOT.I) iferous segments. He described a gill as 



are retracted, leaving slits on the , p i i> i nr>, 



surface of the segment. consisting ot a cluster of about fifteen 



simple cirri, and noted that the tail, which 



formed about one-third of the total length of each worm, was 

 without tubercles or other appendages. Murdoch gave no figures 

 and no other information regarding his species, which was therefore 

 defined insufficiently. Prof, von Marenzeller (1888) * held that, accord- 

 ing to the characters mentioned by the author, this species was 

 not separable from A. marina, a view shared by Saint Joseph 

 (1894) 2 and Prof. Elilers (1901) 3 ; but Profs. Mesnil (1897) and 

 Fauvel (1899) considered A. glacicdis as a synonym of A. cristata.* 



1 Zool. Jahrb. Abt. Syst., iii (1888), p. 15. 



2 Ann. Sci. Nat. Zool., ser. 7, xvii (1894), p. 123. 



3 Fests. K. Ges. Wiss. Gottingen (1901), p. 176. 



4 References to these two papers are given in the synonymy of A. cristata 

 (p. 106). 



[lor. 1 



