KOONSIA. 221 



bipinnate, folded down the center so as to expose one side only, the 

 stalk without the pinnae within, attached to the body as far as the 

 16th filament; pinnae 24, rapidly increasing in length from the ante- 

 rior to the 6th, thence gradually decreasing to the posterior end, 

 each filament attached beneath for more than half its length ; mid- 

 rib beaded at the junction of each plumelet. Anus just within the 

 tip of the gill and behind the membrane upon which it is hung. 

 External genitalia located immediately before the branchia, wrapped 

 within two oblong flaps. (Hedley). 



Of Stokes Point, Broken Bay, N. S. W. (Hill); a mile south of 

 Sow and Pigs Reef, Port Jackson, N. S. W., Australia, in 8 fms. 

 (Field Nat. Soc. N. S. W.) ; Port Stephens, N. S. W. (Brazier). 



Oscanius hilli HEDLEY, Proc. Linn. Soc. N. S. W., (2), ix, p. 127, 

 pi. 7, f. 1,2 (April 25, 1894). 



The figures are copied from Hedley's, drawn from spirit spec- 

 imens. Fig. 18, ventral view, the free edge of foot bent over to ex- 

 pose the anus, gill-plume and genitalia ; on the sole is seen the tail 

 gland. Fig. 19, dorsal aspect. 



Genus KOONSIA Verrill, 1882. 



Koonsia VER., Trans. Conn. Acad. Arts and Sciences, v, p. 545. 

 Pleurobranchillus BERGH, Res. Camp. Sci. Albert I, fasc. iv, 

 1893, p. 27. 



Like Pleurobranchcea in characters of the head, tentacles, pro- 

 boscis, gill, tail-gland and tail-papilla ; differing from Pleura branchcea 

 in having the mantle-edge projecting and overhanging both on the 

 sides and behind, with a wide groove between it and the foot poste- 

 riorly as well as laterally, but in front the mantle passes directly 

 into the veil. Genital openings as in Pleurobranchus. Gill free 

 for the greater part of its length. No shell. Type K. obesa. 



Dentition like that of Pleurobranchcea. 



Distribution : temperate Atlantic in deep water. 



Koonsia is very closely allied to Pleurobranchcea, but it is a less 

 specialized type, in having the mantle edges developed and free, as 

 in the more normal genus Pleurobranchus. Bergh's genus Pleuro- 

 branchillus seems to be absolutely synonymous with the group defined 

 by Verrill ten years earlier. 



