154 THE ANNELIDA POLYCHAETA. 



for detailed description or comparison. The conical head ends in a short trans- 

 parent tubercle, which is not abruptly set off. The anal cirri are large and leaf- 

 like, broader than represented by figures of kowaleivskii, and particularly for young 

 specimens in which these structures are commonly much reduced. Nearly 

 all of the cirri have been rubbed off. The number of somites is small, and the 

 specimen is probably not mature. 



Locality. Off Cape San Lazaro, Lower California: Sta. 4580 (lat. 24° 

 55' N., long. 112° 45' W.). 300 fms. to surface. Surface temp. 76° F. 10 

 October, 1904. One specimen. 



Plotobia, gen. nov.^ 



Prostomium conical. Tentacle short, but sharply distinct from the pros- 

 tomium, though the latter narrows conspicuously forward to the base of the 

 tentacle. Without definite flagella-bearing ridges. Bearing the usual pair of 

 foliaceous cirri, these pertaining apparently to the peristomium, which is almost 

 completely fused above with the prostomium. 



The first free somite bearing a middorsal prominence, on each side of which 

 is a branchiform appendage which may be either simple and cirriform or con- 

 spicuously branched. In addition this somite and the second one bear each a 

 single pair of foliaceous cirri. 



From the third free somite caudad both dorsal and ventral foliaceous cirri 

 are present, there widely separated, with midway between them the setigerous 

 lobe. 



The number of somites twenty-one. Length up to 32 mm. 



Genotype. — Plotobia coniceps, sp. nov. 



This seems nearer to Sagitella than to any other of the three previously 

 known genera. The possession of the branchiform nuchal appendages on the 

 first somite seems clearly to separate it from this as well as from the other genera. 

 In the literature pertaining to those species not seen by me I find no mention 

 of structures comparable to these. Plotobia is like Sagitella in the character- 

 istically conical form of the prostomium and in having the setae begin on the 

 third free somite (morphologically the fourth) ; aside from the possession of the 

 branchiform organs, it differs, e.g., in the more limited number of somites and 

 in the more abrupt separation of the tentacle. 



' wXuTos, floating, and /3ios, life. 



