368 THE ANNELIDA POLYCHAETA. 



small Mollusca. They have marked powers of regeneration, renewing readily 

 the anterior as well as the posterior region of the body.' 



The littoral habits of these annelids accounts for the fact that but a single 

 species is represented in the collections of the Albatross, this being the 

 widely distributed Boccardia polyhranchia (Haswell). 



Key to Genera. 



a. Fifth (or fourth) sctigerous somite not specially modified. 

 h. With no branchiae. 

 c. Body separated into two sharply distinct regions by difference in setae, the first nine somites 

 bearing simple setae only, the others exclusively hooded crochets; ventral lamellae of more 



or less constant form, or changing but gradually Magelona F. Muller. 



cc. Body not thus divided into two sharply limited regions; ventral lamellae prominent only on 



the first four jiairs of parapodia Spiuphiincs Grube. 



66. Branchiae present. 



c. Prostomium without frontal processes or cornua. 

 d. Branchiae present on the first setigerous somite. 



e. Branchiae on the first somite only Streblospio Webster. 



ee. Branchiae present also on some succeeding somites. 



/. Only four or five pairs of branchiae Prionospio Malmgren. 



//. Numerous branchiae present. 

 (J. These present only on the anterior region of the body. 



Laonice Webster and Benedict. 



(jg. Branchiae continuing to caudal end of body Spio Fabrioius. 



(Id. No branchiae on first setigerous somite, 

 e. Branchiae beginning on the second somite. 

 /. No crochets in notopodia. 

 q. With anal cirri. 



h Hooded crochets beginning on the eighth or ninth somite Microspio Mesnil. 



hit. Hooded crochets beginning on fifteenth somite Mesospio Gravier. 



gg. Anal region cup-shaped, with no cirri Nerinides Mesnil. 



//. Crochets present also in notopodia. 



g. With anal cirri Aonides ClaparMe. 



gg. Anal region cup-shaped, no cirri Nerine Johnston. 



ee. Branchiae beginning caudad of the second somite. 



/. Dorsal lamella free from the branchia Spionides Webster and Benedict. 



//. Dorsal lamella fused with the branchia Pygospio Claparede. 



cc. Prostomium with frontal processes. 

 d. Branchiae on first setigerous somite. 

 c. Branchiae throughout length of body; no hooded crochets in notopodia. 

 /. Body divided into two regions by a specialized somite, the sixteenth; dorsal cirri 

 present on first four somites in addition to branchiae; a stout hooked seta on jiara- 



jiodia of first pair Morants Chamberlin. 



ff. Not so Scolelepis Blainville. 



ee. Branchiae absent from posterior region of body; hooded crochets also in notopodia. 



Scolecnlepides Ehlers. 

 dd. Branchiae beginning on second setigerous somite (hooded crochets in notopodia). 



MarcuzcUcria Mesnil. 

 (/((. I'jithcr the fifth or the fourth setigerous somite specially modified. 

 6. The fifth somite specially modified, bearing stout paleae. 



c. Branchiae beginning on the second setigerous somite Boccardia Carazzi. 



' CJ. Mesnil Bull, scient., 1897, 29, p. 201, 209. Also Nussbaum, Zeitschr. wiss. zool., 190.5, 79, pi. 

 13-10; Giard, Compt. rend Assoc. Frangai.se, 1901, p. 153. 



