CENOGENUS DESCENDENS. 333 



Cenogenus, gen. nov.^ 



Prostomium conical, smooth, devoid of processes and eyes. 



Two first somites lacking parapodia and setae. A conical nuchal process 

 present at anterior edge of first segment above, this often retracted. 



Four pairs of maxillae present, these well-developed plates, but all edentate, 

 or the second alone with dentiform processes. First pair in form of strong 

 hooks; carriers short, without slender posterior supports, or these obsolete. 



Mandibles united mesally in the broad anterior region, where they have 

 well-developed dental plates; stems slender and short, tapering caudad. 



Parapodia essentially uniramous. Distally with a short, finger-like, post- 

 setal process, but with no presetal process. Notocirri abortive. 



All setae simple, in anterior region exclusively of a slender hmbate form, 

 but in posterior region with in addition a single, stout, crochet-formed, hooded 

 seta in each parapodium, the guards of this rounded and short. 



Genotype. — d descendens, sp. nov. 



Cenogenus descendens, sp. nov. 



The body is but little narrowed cephalad, more strongly so caudad. 

 Strongly convex dorsally, notably less so ventrally. 



Prostomium conical, broader than deep, and sometimes appearing much 

 compressed dorsoventrally ; short, the width equalling or exceeding the length. 

 Smooth throughout. The anterior region flattened, or sometimes a little con- 

 cave beneath in front of a moderately bulging basal region. Much exceeding 

 the combined length of the first two segments. 



Peristomium set off by a deep sulcus from the prostomium. Dorsally it 

 is twice as long as the second somite. Beneath it usually protrudes ventrad 

 as a swollen transverse ridge, or lower lip, with a rounded lobe extending forward 

 at each end and curving about the mouth to meet that of the other end in the 

 front of the mouth-opening. Swollen all the way around, so as to rise above 

 the level of the second somite dorsally also. Narrowest at sides where it is 

 crossed longitudinally by a few sulci. Second somite longer dorsally than 

 ventrally. 



Succeeding somites simple, regular, and smooth. They are of almost 

 uniform length from the first setigerous caudad, all short. 



Form of pygidium unknown. 



'^ KaivSs, strange, and yipvs, jaw. 



