NEREIS CAENOCIRRUS. 209 



Nereis caenocirrus, sp. nov.'^ 

 Plate 33, fig. 7, 8; Plate 34, fig. 1-G; Plate 35, fig. 1, 2. 



The body in general is colorless, or weakly brownish, probably from preser- 

 vation, the nereid division in particular being translucent. Eyes black. Ten- 

 tacles and cirri colorless and translucent. Setae also colorless and transparent. 



The larger type-specimen is 16 mm. long with the maximum width, exclusive 

 of parapodia, 1.6 mm., and inclusive of parapodia and setae, 3.4 mm. The body 

 is constricted at the junction of its two principal divisions. The nereid division 

 narrows strongly cephalad and less markedly at its caudal end. The hetero- 

 nereid division is widest a little in front of its middle from where it narrows 

 shghtly forward and gradually and strongly caudad. The number of somites 

 in the nereid division is fifteen and in the heteronereid division fifty-five and 

 sixty, making the total number in the two types seventy and seventy-five respec- 

 tively. 



The prostomium consists of a principal, posterior, ocular division, quadrangu- 

 lar in outHne as seen from above, and a low, subtriangular, apically rounded pre- 

 ocular division. Its length is about three fourths the width and is greater 

 than the combined length of the first three somites, but less than that of the first 

 four. The four eyes are of but moderate size and are very nearly equal, the 

 anterior ones being slightly larger. The eyes of each of the two pairs are sepa- 

 rated by an equal distance. The eyes on each side are contiguous, with the ante- 

 rior one cephaloventrad from the posterior. The lens of each posterior eye is 

 directed a little ectad of dorsad. Each anterior eye is more lateral in position, 

 with the length directed cephaloectad. The tentacles are attached beneath the 

 anterior end of the prostomium and project directly ventrad. They are slender, 

 tapered and short, about equalling the length of the proximal article of the 

 palps. The palps are attached on the ventral surface between the anterior 

 eyes, which they exceed in diameter. They are separated mesally and project 

 directly ventrad. The proximal article in each is stout, cylindrical and long, 

 while the distal article is abruptly much narrower, and short and rounded. 

 (Plate 34, fig. 1). 



The peristomium above presents an anterior border of wide, but very low, 

 triangular form. The apical angle very obtuse. The somite is divided by a 

 deep transverse sulcus which is weak laterally but is again strong ventrally. 



' Kaiuos stran,j;c, and cirrus. 



