CLASSIFICATION. 21 



j. Body posteriorly with a conspicuous paired sternal plate, from the edges of 



which radiate numerous fascicles of long slender setae Slernaspidae. 



jj. Body without this structure. 



k. Palpi present, greatly elongate and tentaculiform Spionoidea. 



I. First parapodia greatly developed, directed forwards and bearing long 

 setae which meet in the middle in front of the head; short spines or 

 crochets present on somites II and III and sometimes IV. .Disomididae. 

 II. First parapodia not thus directed forward and bearing setae that cross in 

 front; no stout spines on somites II, III, or IV. 

 m. Parapodia distinctly biramous, with notopodial setae freely protrud- 

 ing; a lamina caudad of each setigerous ramus; no ligula or inter- 

 mediate branchia above neuropodium Spionidae. 



mm. Notopodia represented by dorsal branchiae in the bases of which the 

 setae are concealed; no laminae caudad of setigerous rami; a ligula 

 or branchia just above each neuropodium of the first seven pairs. 



A pislhobranchidae. 

 kk. No such palpi present on the prostomium. 



I. Body with a distinct thorax of nine to fourteen somites in which the 

 parapodia are uniramous and bear only simple hastate or lanceolate 

 setae or paleae; the remaining part of body having parapodia biramous 

 with neuropodia in the form of uncinigerous tori, this region in most 

 with its anterior five, or less commonly but two, somites differentiated 



into a median region Chaetopteridae. 



II. Not so. 



TO. Integument in considerable part strongly roughened or tesselated. 

 Body short; somites annulated; branchiae when present few and 



anterior in position Scalibregmidae. 



mm. Integument not thus roughened; branchiae when present more 

 numerous. 

 n. Branchiae none; cirri, excepting certain special anterior ones, very 



short and stumpy, two-jointed Pisionidae. 



nn. Branchiae present; cirri when present not of this form. 



o. Setae and branchiae throughout strictly lateral in position; body 

 short, of few somites, these commonly annulated .... Opheliidae. 

 00. Branchiae dorsal or subdorsal in position; body elongate, consisting 

 of numerous, short, simple somites. 

 p. Parapodia present as distinct setigerous prominences; cirri 

 present. Body flattened dorsally, rounded ventrally; bran- 

 chiae usually ligula te. 

 q. Setae strongly cross-striate or annulated; no crochets in 



posterior region; anal cirri two or four Ariciidae. 



qq. Setae not annulated; crochets in posterior region; cirri three. 



Paraonidae. 

 pp. No distinct setigerous or parapodial prominences and no cirri; 

 body convex dorsally; branchiae long and filiform and present 

 on many or a considerable number of somites . . Cirratulidae. 

 i. Prostomium bearing true tentacles or palpi of ordinary form, or both tentacles 

 and palpi. 

 j. Notopodial setae blade-like, strongly cross-striate, and arranged in radiate or 

 palmate groups along each side of the dorsum which they cover wholly or 

 in part. 

 k. Notopodia, at least in part, with capillary setae as well as paleae; noto- 

 cirri on somites separated by one or more not bearing them . . Palmyridae. 

 kk. Notopodia with paleae exclusively; notocirri on all parapodia. 



Chrysopetalidae. 



jj. Parapodia not thus differing in character on alternate somites; notopodial 



setae not of this structure and arrangement. 



k. Both notopodium and neuropodium bearing a conspicuous lamella on its 



edge in addition to the cirrus; notopodium also bearing a branchia which 



is cirriform. 



