NO. 3 HARTMAN : ORBINIIDAE, APISTOBRANCHIDAE, PARAONIDAE 219 



(see Jeener, 1927, pp. 104, 110 and Rullier, 1950, pp. 226-231). The 

 presence of lateral organs has been noted in Scoloplos armiger, Orbinia 

 latreillii, Phylo foetida, Naineris laevigata, Scolaricia typica, Proto- 

 aricia oerstedi and possibly others. They are absent in species where an 

 interramal cirrus is present and are considered homologous to the latter. 

 Both are modifications of the epithelium and have no relation to nuchal 

 organs. 



Branchiae are conspicuous, segmentally paired processes and present 

 on most body segments; they are absent from a few (two to five) to 

 many (about 30) anterior segments and rarely altogether absent 

 (Orbiniella) . The first few pairs may be small and papillar, located on 

 the dorsolateral side of the body within the notopodial bases. They 

 enlarge gradually or abruptly and become long, subcylindrical to flat- 

 tened lobes that are much larger than the accompanying parapodial 

 lobes. Their lateral margins are more or less conspicuously fimbriated 

 or ciliated except for a smooth tapering distal end which may be set off 

 from the fimbriated region by a subdistal swelling (pi. 23, fig. 2). In 

 most species the branchiae are simple; in a few they are branched (pi. 

 33, fig. 2). 



Dorsal ciliated ridges are present in genera in which a middorsal 

 space separates the inner branchial bases, as in Naineris and Protoaricia. 

 They are more restricted or nearly absent when the branchial bases are 

 close together middorsally. The ciliary rows are more or less continuous 

 with the rows that border the branchial pairs. 



Dorsal ciliated mounds (= dorsal organs of Rullier, 1950) homo- 

 logous with the nuchal organs of the prostomium are segmental and 

 present on most or perhaps all segments. They are located in front of 

 the branchial bases nearer the segmental groove. Each organ is a ciliated, 

 retractile mound developed from epithelium. A pair may be far apart, as 

 in species of Naineris (pi. 38, figs. 1 and 6) and Protoaricia, or nearer 

 together as in species of other genera. They may be circular, oval or 

 shield-shaped as in Scoloplos and Scolaricia, or slitlike depressions as in 

 Orbinia and Phylo. They may be recognized externally by a circlet of 

 dark pigment about their bases. Rullier (1950, pp. 220-225) has de- 

 scribed them as groups of ciliated cells with innervation like that of the 

 nuchal organs. 



Statocysts or organs of equilibrium are known for some species of 

 Naineris and Protoaricia. They are segmental, epithelial depressions, 

 sometimes covered with a thin membrane, located on a variable number 



