264 THE ANNELIDA POLYCHAETA. 



composed of numerous simple somites, and with a smooth and iridescent skin. 



The prostomium differs from that of the Leodicidae in bearing always two 

 frontal tentacles in addition to five posterior ones, the total being uniformly 

 seven. Palpi present. Eyes two, or none. 



The peristomium differs from that of the preceding family in being uni- 

 formly entire, with no trace of biannulation. Tentacular nuchal cirri may be 

 present as a single pair, or absent. 



Branchiae either present or absent, when present either simple filaments 

 or variously branched. Parapodia and setae in general as in the Leodicidae, 

 as are the other more important structural characters. 



Unlike the Leodicidae, almost all members of this family occur at consider- 

 able and great depths, a number of species, such as Leptoecia ahyssorum (p. 320), 

 occurring below the two thousand fathom line. The tubes are sometimes 

 composed exclusively of the hardened secretion from the animal, as is the case 

 with the remarkable, tough, horny and hyaline, quill-like tubes of Hyalinoecia 

 giving the name to that genus. In other cases the secretion forms but a com- 

 paratively thin hning membrane strengthened with a wall composed of various 

 foreign objects, such as the long fibers, or spicules, of vitreous sponges, as in the 

 case of Onuphis sombreriana Mcintosh, the shells of various Foraminifera and 

 similar forms, as in the case of Paronuphis solenotecton (p. 310), or simply of 

 fine mud, as in 0. proalopus, sp. nov., and 0. cobra, sp. nov. 



Key to Genera. 



a. Branchiae present. 

 6. With tentacular cirri. 



c. The frontal tentacles long and slender like the others Heptaceras Ehlers. 



cc. Frontal tentacles short, stumpy. 



d. With especially long simple setae in first three pairs of parapodia . . Rhamphobrachium Ehlers. 

 dd. Without long simple setae on first three setigerous somites. 



e. Branchiae simply cirriform or pectinate; eyes small, point^like, between median and 



posterior paired tentacles on each side Onuphis Audouin and Milne Edwards. 



/. First two pairs of parapodia not prolonged. 



//. First two pairs of parapodia prolonged, extending forward beneath the prostomium. 



Paranorthia Moore. 



ee. Branchiae in the form of a brush or plume, the filaments spirally arranged, the largest 



ones at the anterior end of the series ; eyes large, between unpaired tentacle and median 



lateral on each side Diopaira Audouin and Milne Edwards. 



bb. No tentacular cirri; brancliiae cirriform Hyalinoecia Makngren. 



aa. With no branchiae. 

 6. With tentacular cirri. 

 c. Eyes large, each between unpaired tentacle and median lateral one of corresponding side. 



Paradiopatra Ehlers. 

 cc. Eyes small, punctiform, each situated laterally between the median and posterior lateral 



tentacle Paronuphis Ehlers. 



bb. With no tentacular cirri Leptoecia, gen. nov 



