194 THE ANNELIDA POLYCHAETA. 



sponges or the stalks of decaying sea-weeds. They are not infrequent in the 

 coralline and laminarian regions. As a rule they rapidly reform their com- 

 monly thin, transparent and often collapsible tubes when released in an aquarium. 

 While most nereids are strictly marine, some may live in brackish and even in 

 fresh water, such being the case with most of the species of Namanereis (com- 

 monly designated Lycastis) . A species of the closely related genus Lycastoides, 

 L. alticola Johnson, was found in a fresh water stream of southern Cahfornia 

 at an altitude 7,000 feet above sea-level (Cf. Ehlers, Nach. K. gesselsch. wiss. 

 Gottingen. Math. phys. klasse, 1897, p. 70; Gravier, Bull. Soc. hist. nat. 

 Autun, 1901, 14, p. 29; Johnson, Mark anniversary vol., 1903, p. 210). Some 

 forms are commensal, such as Nereis fucata and others which live with the hermit- 

 crab in shells of Buccinum, etc. {Cf. Mcintosh, British annelids, 1910, 2, pt. 1, 

 p. 259; Harrington, Trans. N. Y. acad. sci., 1898, 16, p. 214). 



Some nereids live largely upon Algae, such being the case with Nereis cul- 

 trifera Grube and A'^. pelagica Linne. In addition the members of the family 

 feed upon small ova, sponges, Crustacea, and also upon other anneUds. 



Key to Genera. 



a. Tentacles arising from a very long common basal article inserted anteromesally on the prostomium. 



(Pelagic form) Kainonereis, gen. nov. 



aa. Tentacles with no such common basal article. 

 6. Proboscis with no paragnatha. 



c. Nereids with dendritic branchiae Dendronereis Peters. 



cc. With no dendritic branchiae. 

 d. Noto)5odium rudimentary. 

 e. Prostomium anteriorly deeply incised; tentacular cirri on each side arising from an elon- 

 gate common basal article Lycastoides Johnson. 



ce. Prostomium anteriorly not thus deeply incised; tentacular cirri not arising on each side 



from a long common basal article Nainanereis, gen. nov.' 



dd. Notopodium well developed. 



e. Peristomiuni with parapodia and setae Micronereis Claparede. 



ee. Peristomiuni witliout parapodia or setae Lepionereis Kinberg. 



&6. Proboscis with paragnatha. 

 c. Paragnatha all soft (papillae). 



d. Setae of two lands; eyes none Chaunorhynchus, nom. nov.^ 



dd. Setae all of one kind, homogomphs; four eyes present Tylonereis Fauvel. 



cc. Hard, chitinous or callous paragnatha present. 



d. Paragnatha all simply hard or callous TyUcirhyiichus Grube. 



dd. Horny or chitinous paragnatha present. 



e. Both chitinous and soft paragnatha present Leonnaies Kinberg. 



ee. Paragnatha all chitinous. 



/. Paragnatha conical, all separated from each other. 

 g. Paragnatha occurring on both rings of the proboscis. 



' vaiia, a stream or spring, in allusion to the occurrence of most species of this genus in fresh and 

 brackish water. 



- Pro Ceratocephale or, as commonly, Ceratocephala, Malmgrcn, preoccupied in Crustacea, xawoj, 

 gaping, flaccid, and piiyxos, snout. 



