740 



" THETIS " SCIENTIFIC KKSULTS. 



Actmometra jukesii, 1879, P. H. Carpenter, Proc. Koy. Soc, vol. 

 28, p. 390 (North-east Coast of Australia). 



Actinometra jukesi, 1884, Bell, Rep. Zool. Coll. H.M.S. "Alert,"' 

 p. \QS (Albaiiy Island; Prince of Wales Chanitel) ; 1885, 

 Proc. Linn. Soc. N. S. Wales, vul. 9, p. 49« {Port Molle): 



Actinometra paucicirra, 1884, Bell, torn, cit., p. 169, pi. xvii., figs. 

 A, Art (Primce of Wales Channel; Thursday Island); 

 1888, P. H. Carpenter, " Challenger " Reports, Zool., vol. 

 26, p. 291. — 1898, Doderlein, Deukschr. Ges. Jena, vol. viii., 

 p. 479 {TMirsday Island). 



Differential Characters. — Tiiis species always lias almost or 

 quite exactly twenty arms and division series of two ossicles each,, 

 united by a pseudo-sjzygy wiiich appears exactly like a wyzygy 

 externally. When adult there are no cirri ; the cirri of the 

 young are always perfectly smooth dorsally. 



Specimens in the Australian Museum Collection. — Albany 

 Passage : — Two fine examples, one with nineteen, the other with 

 twenty arms. Port Molle, Queensland: — Two specimens; one is 

 a fine large individual with twenty arms 120 mm. long, the other 

 a young example with twenty arms 60 mm. long, and cirri vii, 

 15, 11 mm. long. This specimen represents the stage figured by 

 Bell in the "Alert" Report (pi. xvii., A); the seven cirri are 

 confined to the interradial angles of the centrodorsal ; three are 

 single, the remaining four in two paii's ; they are moderately 

 slender; the first segment is very short, the second not quite so 

 long as broad, the third slightly longer than broad, the fourth 

 and following approximately equal in size, about half again as 

 long as broad except the penultimate, which is about as long as 

 broad ; the more proximal segments are slightly constricted 

 centrally, and the penultimate bears a small and short sub- 

 terminal opposing spine ; the terminal claw is half again as long 

 as the penultimate segment, moderately and evenly curved. 



The study of these specimens has shown tliat in this species,. 

 as in the genus Comaiella, arm division is of the so-called 

 " compound " type, and in Comatula pecti7iata also when a II .Br 

 series occurs the first true syzygy on the inner arm is between 

 the first and second brachials, on the outer between the third 

 and fourth. The very characteristic cirri, identical in small speci- 

 mens of rotalaria and in specimens of- the other species of the 

 genus at comparable stages, which never show any trace of dorsal 

 processes on the outer segments, and which have all the segments 

 except the basal subequal with no transition segments, as well as 

 the invariably ten-armed condition of all but three of the species, 

 one of which is almost invariably ten-armed, show that Comatula 



