624 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Genus MELINNA Malm gr en. 



MELINNA DU3ITA, new species. 



Plate 51, figs. 13-16. 



Type. — Cat. No. 18957, U.S.N.M. Fragmentary but possessing im- 

 portant diagnostic characters. Sixteen somites present. Length, ex- 

 clusive of gills and tentacles, 15 mm.; greatest width (across third 

 somite), 7 mm. 



Prostomium directed anteriorly and slightly ventrally, ending in 

 folded upper lip. Tentacles of two kinds. Posterior (figs. 13-14) 

 six in number, arising together from the dossal surface of the pros- 

 tomium just behind the upper lip. Greatest length of a complete 

 posterior tentacle, 15 mm. Those tentacles are deeply grooved along 

 one side — a condition not easily seen because of coiling. Anterior 

 tentacles (fig. 13) with diameter equal to one-third that of posterior 

 tentacles, arising in two groups of seven on each side of upper lip: 

 varying in length from 3 to 7 mm. 



"Buccal segment" or lower lip (fig. 13) largely covered by fol- 

 lowing somite, hut showing as an oval pad just ventral to the mouth 

 opening. Dorso-lateral extremities of lower lip arising immediately 

 in front of the origin of the gills. 



Next four somites forming a collar-like structure with promi- 

 nently developed lateral region extending obliquely from ventral 

 to dorsal surface. Free edge of first somite lying immediately 

 beneath the low T er lip. First two somites marked ventrally (fig. 13) 

 by row of fine setae (fig. 16). Third somite with similar setae ven- 

 trally, and delicate tuft of similar but larger capillary setae dorsally. 

 Fourth somite similar to third, but with prominent seta tuft dor- 

 sally (fig. 14). Third somite plainly continuous dorsally (fig. 14), 

 forming an inconspicuous or else strongly retracted post-branchial 

 ridge. No trace of the hooks figured by Marenzeller (1874) for 

 M. adriatica was found. 



Gills stout, tapering, and curved distally (two are broken in fig. 

 14) ; eight in number, arising from the second and third somites. 

 Most anterior gills situated internally on second somite. Other 

 gills situated externally on second and third somites. 



Pinnulae beginning on fifth somite. Second and third pinnulae 

 larger than first, gradually decreasing until on the sixteenth somite 

 they occur as blunt, medianly directed processes. Dorsal setae sine 

 pie capillary, unequal in length, borne on truncated, papillae-like 

 processes. Uncini (fig. 15) pectinate in form, with four large teeth 

 above the ligament process. 



Tube composed of tough inner membrane and thick outer coating 

 of fine brown mud. Total diameter, 1-3 mm. Lumen, 5 mm. 



