SABELLIDJB. 219 



a. Basal lamellae of the branchiae always in a spire. 



a. The two divisions of the branchiae unequal; dorsal bristles of one kind — 



Spirogr aphis, Viv. 



b. The two divisions of the branchiae equal; dorsal bristles of two kinds on the 



thorax — Bispi ra, Kr . 



b. The basal lamellae of the branchiae are not spiral. 



a. No sub-terminal eyes on the branchiae. 



a. Dorsal bristles on the thorax of one kind — Sabella, L. 

 (3. Dorsal bristles of two kinds on the thorax. 



jS 1 . Abdominal bristles of one kind — Potamilla, Mgrn. 

 /3 2 . Abdominal bristles of two kinds. 



Bristles of the first thoracic segment in a linear series — directed 

 towards the head. The posterior base of all the avicular hooks 

 short — Hypsicomus, Grube. 

 Bristles of the first thoracic segment forming an ordinary fascicle. 

 Posterior base of the thoracic hooks very long — Potamis, 

 Ehlers. 



b. Sub -terminal eyes on branchiae. 



Dorsal bristles of one kind on the thorax — Branchiomma, Koll. 

 2. Without a collar. 



Dorsal bristles of two kinds on the thorax — Amphiglena, Clap. 

 I b. Two rows of hooks and bristles on the abdominal tori; 



Bristles of the first thoracic segment disposed in two oblique rows. Thoracic 

 and abdominal bristles of two kinds — Protidides, Webster. 

 II. Thoracic hooks avicular or with a long shaft and in a single row. A single row 

 of avicular hooks on the abdominal tori. 



A. Avicular hooks on the thorax. Avicular hooks on the abdomen. 



a. Branchiae with dorsal appendices. Thoracic dorsal bristles of one kind — 



Dasychone, Sars. 



b. Branchiae without dorsal appendices. 



a. Thoracic dorsal bristles of two kinds. 



a'. Absent on the first segment. Posterior base of all the hooks 



truncate — Laonome, Mgrn. (non Kbg.). 

 a". Disposed in an angular double row on the first segment. Poste- 

 rior base of all the hooks ordinary — Notaulax, Tauber, Lev. 

 (5. Thoracic dorsal bristles of one kind. 



1 a. Branchial lobes forming on each side a double concentric 



half-circle — Sabellastarte, Kr. 



2 a. Branchial lobes do not form a double concentric half-circle — 



HJurato, St.J. 



B. Thoracic hooks with a long shaft 



1 a. Abdominal hooks with a long manubrium ; thoracic dorsal bristles of one 

 j^d — Haplobranchus, Bourne {ManayunHa, Leidy). 



