NER-EIS. 145 



head a certain number of tentacula, more or less developed, and 

 similar in structure to the superior cirrus of the foot. 



The feet form a protuberant series of setigerous lobules along each 

 side ; and they do not differ essentially, although the appendages 

 may be more developed on a certain number than on others. In 

 general each foot is divided into two distinct branches. The bristles 

 with which they are armed are mostly compound ; and to each 

 brush of them there is a spine of the usual form. The cirri are 

 usually filiform or subulate, but in some genera they are transformed 

 into compressed laminae or leaflets. The branchise are simple in 

 structure. Their existence is sometimes doubtful, but more gene- 

 rally they are detected in the guise of lobules or tonguelets on the 

 feet, distinguished from the feet's proper lobes by being destitute of 

 bristles or any armature. 



Synopsis of Genera. 



1 1 . Nereis. Feet homologous. 



12. Nereilepas. Feet nearly homologous; the hinder ones most 



developed. 



13. Heteronereis. Feet dissimilar ; the hinder ones with foliaceous 



lamellae. 



11. NEREIS. 



Nereis ( — ), Cuv. Regn. Anim. iii. 201. Aud. 8^ M.-Edw. Lift, de la 

 France, ii. 184. Johnston in Ann. Nat. Hist. iii. 289, and v. 168. 

 Williams in Rep. Brit. Assoc. 1851, 197, 211, 231, and in Ann. ^' 

 Mag. Nat. Hist. ser. 2. xii. 401, 



Lycoris ( — ), Lam. An. s. Vert. v. 311. Savign. Syst. Annel. 29. 



Nereis, Oersted, Annul. Dan. Consp. 21 ; Grcenl. Annul. Dorsihr. 22. 



Char. Segments all similar in form, with nearly similar feet ; the 

 dorsal cirrus without a mammillate lobe at its base, and no lobule 

 beneath the ventral cirrus : no branchial laminae on the feet : ter- 

 minal piece of the bristles acicular in the upper brush, and acicular 

 and falcate in the lower brush. 



The body of the Nereis is always vermiform, insensibly tapered 

 towards the tail, somewhat truncate in front, and composed of nume- 

 rous narrow segments. The back roundish, but the ventral surface 

 is flattened, and marked down the middle with an impressed line. 

 The head is distinct, a little contracted in front, and furnished with 

 two pairs of eyes placed on the occiput, the one before the other. 

 The small subulate anteunse are inserted on its frontal margin 

 (PI. XV. fig. 1 a, a) ; and, in general, we find two of these organs, 

 which are guarded on each side by a thick palpus distinctly formed 

 of two articulations, the apical capable of being retracted within the 

 other (fig. 1 ft,p)- The large cylindrical exsertile proboscis is divided 



