SPIONIDAE. 367 



The membranous tubes are of the usual form and proportions. They were 

 evidently found buried in shell-beds, as numerous fragments of shells closely 

 cover the walls of the tubes, from which they stand out horizontally. 



Spionidae. 



In the members of this family the body, as a rule, is small, cyUndrical, and 

 translucent, of varied and often bright colors, with the somites numerous. 



The prostomium is small, reduced to a narrow dorsal band, which may 

 extend as far caudad as the fourth somite, though in some cases reaching only 

 the second. Anteriorly it may be entire, or it may be somewhat incised, and 

 thus with two short processes, but with no true tentacles. The eyes are most 

 commonly four, sometimes more and at others wholly missing. Two elongate, 

 tentaculiform, very contractile, and in most easily lost, palpi form a very charac- 

 teristic feature of this family together with the Disomididae and Apistho- 

 branchidae (Spionoidea) . 



Peristomium without processes or setae. Proboscis short and simple, 

 scarcely truly differentiated, but in some, at least, protrusible. 



Parapodia mostly biramous, both notopodium and neuropodium with a 

 distinct lamella caudad of the setigerous branch, which bears two transverse 

 series of setae. 



Setae all simple, of two principal kinds: — finer, limbate, capillary, setae and 

 stout, hooded crochets of a type similar to those occurring in the Capitellidae 

 and some Leodicidae. In addition, special, pale-like spines may occur on the 

 fifth setigerous somite. 



Branchiae simple, ligulate or cirriform, of variable number and position 

 or in some wholly absent, often completely fused with the dorsal lamella. 



Anus more or less clearly dorsal in position, surrounded with cirri, papillae, 

 or a cup-hke rim. 



These forms are almost strictly confined to the littoral region, one species, 

 Nerine foliosa Sars, however, having been dredged from a depth of 725 fathoms. 

 The larvae are widely distributed as pelagic forms, a considerable number of 

 which have been described, though in most cases without definite reference to 

 the corresponding adults. The period of pelagic life seems to be long. Some 

 species live on sandy bottoms of varied character, in beds of mollusc shells, 

 among rocks, and among Algae; others make tubes of sand or calcareous parti- 

 cles. They feed upon diatoms, various other Algae, and such animal forms as 



