200 
notopodium bearing capillary sete and a. transversely 
thickened neuropodium bearing a vertical row of crotchets. 
In the chietigerous region, except in the first three seg- 
ments, there are four annuli between successive cheti- 
gerous 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. 
cla paredit). 
The genus is divisible into a caudate and an ecaudate 
section, 
I.—The characters of the caudate Arenicolidze 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 chetigerous 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 (7.e., not deeply notched as in the 
ecaudate Arenicolide). Gonads small, ova discoidal, 
vitelline membrane comparatively thin (1 to 8). 
(a) A. marina, Linneus. Nineteen chetigerous seg- 
ments. Thirteen pairs of gills; the first, which is on the 
seventh segment, may be reduced (or suppressed). Otoeysts 
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- 
