22 THE ANNELIDA POLYCHAETA. 



Prostomium reduced, mostly quadrangular or rhomboidal with one or 



two pairs of small tentacles on its anterior margin Nepthydidae. 



kk. Parapodia without such lamella on its rami; branchiae never cirriform, 

 but arborescent, pennatifid or none. 

 I. Mouth shifted caudad and bordered by several similarly formed somites; 

 prostomium often appearing as a dorsal caruncle extending over several 



somites Amphinomoidea. 



111. Branchiae none Spintheridae. 



mm. Branchiae present. 



n. Setae and arborescent branchiae forming a broad band on each side 

 of the dorsum over its entire length, leaving naked only a narrow 



stripe along the middle Euphrosynidae. 



nn. Branchiae and setae not forming such broad dorsal bands. 



A mphinomidae. 



II. Mouth not thus shifted back and bordered by several similar somites; 



prostomium not forming a dorsal band or caruncle; branchiae never in 



connection with parapodia. 



m. Integument roughened, strongly papillose; with numerous short 



branchiae on peristomium •. Chlorhaemidae. 



mm. Integument smooth or at least not papillose; branchiae none. 



n. Cirri flattened, foliaceous, and usually containing conspicuous mucus 

 glands. 

 0. Cirri fastened near their middles, elytriform. Prostomium conical 

 and with a single median process; no eyes; fused with the 



peristomium which bears a pair of cirri Typhloscolecidae. 



00. Cirri not elytriform; prostomium not fused with the peristomium; 



eyes present Phyllodocoidea. 



p. Eyes very large; nuchal organs rudimentary or absent; uni- 

 formly five tentacles present; tentacular cirri three or five 



pairs; pelagic forms Alciopidae. 



pp. Eyes small or but moderate, as in most polychaetes, or rarely 

 none; nuchal organs well developed. 

 q. Proboscis with two pairs of true jaws; two pairs of tentacles; 



no palpi; one pair of tentacular cirri Lacydoniidae. 



qq. Proboscis without true jaws, being either wholly unarmed or 

 with a number of small chitinous pieces or denticles, 

 r. A pair of palpi present; tentacles none or a single pair; ex- 

 clusively pelagic forms. 



s. Tentacles none; parapodia normal lospilidae. 



ss. A pair of tentacles present; parapodia greatly elongate. 



Pontodoridae. 

 rr. With no palpi. 



s. Tentacles two pairs and in addition often an unpaired 

 tentacle present; eyes and composite setae nearly 



always present Phyllodocidae. 



ss. Tentacles three; eyes none; setae all simple. .Otopsidae. 

 nn. Cirri not flattened or lamellar and not containing, conspicuous mucus 

 glands. 

 0. Palpi massive, two-jointed, with the terminal article small, in- 

 serted well caudad of the pair of tentacles; proboscis consisting 

 of two distinct rings, the distal one of which always bears a pair 

 of maxillae curved toward each other and toothed on the mesal 



edge ; cirri and tentacles simple Nereidae. 



00. Palpi either absent, or when present inserted nearly at the same 

 level as the tentacles, and when biarticulate with the terminal 

 article conspicuously long; proboscis not divided into two suck 

 rings and bearing stout maxillae of this character; cirri and 

 tentacles commonly in whole or in part composed of separate 

 articles, annulated or moniliform Sylloidea, 



