'280 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



notopodium bearing capillary sette and a transversely 

 thickened nenropodium bearing a vertical row of crotchets. 

 In the chsetigerous region, except in the first three seg- 

 ments, there are fonr annuli between successive chseti- 

 gerons annuli. Internally there are three diaphragms at 

 the anterior end of the first, third and fourth segments. 

 The pharynx has no armature. A pair of hearts present 

 placing the gastric vessels in connection with the ventral 

 vessel. There are five, six or thirteen pairs of nephridia. 

 A pair of otocysts lies in the peristomium (absent in A. 

 claparedii). 



The genus is divisible into a caudate and an ecaudate 

 section. 



I. — The characters of the caudate Arenicolidse may be 

 briefly stated thus : A distinct tail present ; the parapodia 

 and gills do not extend to the posterior end of the animal. 

 The body is often swollen anteriorly. Gills pinnate or 

 derivable from the pinnate type, eleven to thirteen pairs, 

 the first (which may be small or even absent) on the 

 seventh or eighth chsetigerous segment. Prostomium 

 consisting of a median and two lateral lobes, brain with 

 distinct anterior, middle and posterior regions. Funnel 

 of nephridium with dorsal lip well provided with flattened, 

 spatulate, ciliated, branched, vascular processes ; ventral 

 lip ciliated, entire [i.e., not deeply notched as in the 

 ecaudate Arenicolidse). Gonads small, ova discoidal, 

 vitelline membrane comparatively thin (1 to 'd/u). 



(a) A. marina, Linnaeus. Nineteen chsetigerous seg- 

 ments. Thirteen pairs of gills; the first, which is on the 

 seventh segment, may be reduced (or suppressed). Otocysts 

 opening to the exterior. Otoliths, numerous foreign bodies 

 (quartz grains, &c.) which may, however, be covered with 

 a layer of secreted chitinoid substance giving them a 

 rounded outline. Six pairs of nephridia opening on seg- 



