354 THE ANNELIDA PQLYCHAETA. 



ated. Stouter, spine-like or clavate, camerated forms may also occur, these 

 being in the neuropodia and confined to the anterior region. 



Branchiae present, these Ugulate in form and dorsal in position. They 

 begin on one of the first twenty somites as rudimentary processes, increasing 

 gradually in size and usually continuing to near the caudal end; often forming 

 two more or less distinct groups. 



Anal cirri two or four, usually long. 



Proboscis short, unarmed, distally simply frilled, or sometimes more dis- 

 tinctly digitate, in some not evaginable. 



Larvae non-pelagic. 



Otocysts, such as occur, among polychaetous annelids, also in the Areni- 

 colidae, Terebellidae, and Sabellidae, are found in some ariciids. When found 

 in this family they occur on a limited number of the anterior somites. Each 

 is an invagination ordinarily close to the notocirrus. Another type of sense- 

 organ, the more widely occurring "lateral ciliated organs" or "lateral line 

 organs," are located farther ventrad and are to be found in all regions of the body.^ 



Ariciids occur from the littoral zone down to considerable depths. Aricia 

 norvegica Sars was dredged by the Challenger from 1,340 fathoms. They 

 frequent mud, and sand more or less mixed with mud. They live upon small 

 organisms and often ingest much foreign matter, their intestines frequently con- 

 taining sand and debris of shells, Foraminifera, etc. (Gravier, Nouv. arch. Mus. 

 hist, nat., 1908, ser. 4, 10, p. 167). 



Key to Genera. 



a. Neuropodium with a laminate, festooned border, opposite ones often joined across the venter. 



Aricia Audouin and Milne Edwards. 

 aa. Neuropodium not so, simply bifid or entire. 



h. Prostomium anteriorly rounded, button-shaped Nainereis Blainville. 



bb. Prostomium pointed. 



c. On some somites of the posterior division each branchia with five or more filaments forming a 

 transverse series and leaving only a narrow middorsal region naked; peristomium strongly 



reduced ventrally Branchethus, gen. nov. 



cc. Branchiae ligulate, never with simple branches in transverse series; peristomium not reduced 

 ventrally Scoloplos Blainville. 



Nainereis Blainville. 



Diet. sci. nat., 1828, 57, p. 491. 



Naidonereis Malmghen, Annulata Polychaeta, 18G7, p. 73; Ehlers, Zeitsch. wiss. zool., 1875, 25, p. 59; 

 McIntosh, Ann. mag. nat. hist., 1905, ser. 7, 15, p. 48. 



1 For an excellent account of the occurrence and structure of otocysts in polychaetes see P. Fauvel, 

 Rocherchcs sur les Otocystes dcs Anndlides Polychctes, Ann. sci. nat., 1907, ser. 9, 6, p. 1-149, 3 plates. 



