KAINONEREIS ALATA. 197 



heteronereis region with foliaceous expansions proximally. In this region also 

 a special, additional foUaceous appendage at tip of the neuropodium and all setae 

 replaced by the larger, paddle-shaped swimming setae. 



Anal cirri two ; annulated. 



Alimentary canal straight. Oesophagus with a pair of caeca. 



Genotype. — K. alata, sp. nov. 



This form is unquestionably very close to Nereis to which its precise rela- 

 tionship can be decided only when the other phases of the type-species are 

 known. It is given separate generic rank here chiefly because of the highly 

 peculiar, long, single process bifm-cate at the tip and which may be morphologi- 

 cally double or else may represent an extremely elongate anterior division of 

 the prostomium, bearing at its tip the two short tentacles; and the elytriform de- 

 velopments, possibly peculiar to the male, on three of the anterior pairs of para- 

 podia, though special developments of parapodial structures are not infrequent 

 in the family. One form of the anterior notopodial setae is quite special, but by 

 itself would scarcely be regarded as of more than specific value. The reduction 

 in size of the palpi is not infrequent in the males of Nereis. 

 • 



Kainonereis alata, sp. nov.^ 



Plate 28, fig. 6-8; Plate 29, fig. 1-8. 



Epitokous or Heteronereis Phase. 



Body-waU colorless and transparent, but the body contents in part giving 

 a brownish tinge. Appendages colorless. Setae colorless and transparent. 



The body is widest near the middle of the length, from where it narrows 

 caudad to a point and cephalad to a much narrower anterior region consisting 

 of five somites in front of the elytrophorous ones. These anterior somites 

 narrow more gi-adually toward the cephalic region. A typical specimen, 10.5 

 mm. long, which seems to be about the average, consists of fifty-six somites. 



The prostomium is short and narrow, clearly deeper dorsoventrally than 

 either the length or the width. The dorsal sm-face anteriorly between the 

 anterior eyes is raised into a conspicuous, low, subcorneal, distally rounded ele- 

 vation which bears at the top two small, transparent, secondary eminences 

 or knobs. It may also be elevated at the posterior end above between the pos- 

 terior eyes. The anterior svirface is incurved at about the middle height above, 



'filatus, winged. 



