18 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 7 



The families considered in this report include the scale-bearing 

 chaetopods and the Pisionidae. The latter family is included because 

 its affinities are with this group, with respect to its proboscidial and 

 prostomial structures. A key to these families follows. 



1. Dorsum provided with elytra which may or may not be con- 

 cealed by a felty covering 2 



1. Dorsum without elj^tra or felt PISIONIDAE 



2. Some segments with dorsal cirri, others with elytra .... 3 



2. All segments with elytra; body long, vermiform 



(not represented in the collections) . . . POLYLEPIDIDAE 



3. Body long, slender, all posterior segments bearing elytra . 

 SIGALIONIDAE 



3, Body long, slender, to short, plump ; posterior segments have 

 elj^tra alternating with dorsal cirri or have no elytra .... 4 



4. Elytra and dorsal cirri alternate more or less regularly through- 

 out ; prostomium with sessile eyes and with or without peduncu- 

 late eyes ; without facial tubercle . POLYODONTIDAE 



4. Elytra and dorsal cirri alternate regularly on anterior seg- 

 ments, but irregularly present on posterior segments or entirely 

 absent 5 



5. Ventral acicula stout, with an expansive chitinous, embedded 

 plate (pi. 23, fig. 280) at its distal end; body short, subrec- 

 tangular; posterior segments without true elj'tra .... 

 PAREULEPIDAE 



5. Ventral acicula without distal expansion; body long or short; 

 posterior segments with or without elytra 6 



6. Proboscis without horny jaw pieces; prostomium with a median 

 antenna; eyes usually stalked (rarely sessile) ; facial tubercle 



well developed; dorsum with or without felt 



APHRODITIDAE 



6. Proboscis with 4 horny jaw pieces at its distal end; pro- 

 stomium with 3 or 2 antennae; eyes sessile; facial tubercle ab- 

 sent or not conspicuous; dorsum without felt covering 

 POLYNOIDAE 



