782 *' THETIS " SCIENTIFIC RESULTS. 



Differential Characters — In its general appearance tliis species 

 is more robust than P. mulleri from New South Wales ; the 

 centrodorsal is thicker and more columnar, the cirri are longer 

 and stouter, and therefore not so slender distally, while in the 

 basal portion of the fully developed cirri the segments are as long 

 as or slightly longer than broad instead of, as in viiilleri, about 

 twice as broad as long ; the proximal pinnules are more enlarged 

 and longer than in mulleri, with considerably longer segments of 

 which the central are half again to twice as long as broad instead 

 of not so long as broad as in P. mulleri ; in the middle pinnules 

 of miilleri the segments do not become longer than broad until 

 the distal quarter is reached, while in the present species the third 

 and following are always longer than broad, and the distal are 

 considerably elongated. In inacronema there is a strong tendency 

 for the cirrus sockets to be arranged in columns, about four in 

 each radial area, a tendency seldom indicated in mulleri. 



Specimens in the Australian Museum Collection. — Kangaroo 

 Island, South Australia — Two fine specimens; one has thirty-two 

 arms 55 mm. to 60 mm. long, and cirri about 1. 82-88, 65 mm. 

 long ; the centrodorsal is 6 mm. high and 8 mm. in diameter ; the 

 III Br series are developed externally in 2, 1, 1, 2 order as is 

 always the case in this group ; the lower pinnules are large and 

 long. 



The other is six-rayed with twenty -six arms, five, four, three, 

 four, six, and four to a post-radial series ; the cirri are about 1. ; 

 the centrodorsal is 5 mm. high and 8 mm. in diameter. 



In both of the specimens most of the cirri are comparatively 

 small and undeveloped. 



Additional Australian Records. — King George Sound ; Dirk 

 Hartog Island, 7 fathoms ; Port Phillip. 



Both this and the succeeding species occur at Port Phillip, 

 according to the labels on the specimens at the British Museum ; 

 this form, however, appears to be much more common, for, while 

 it is represented by thirteen specimens from that locality, Pt. 

 miilleri is only represented by one. 



Remarks. — This species was first described from King George 

 Sound in South-western Australia, from specimens brought back 

 to Paris by MM. Quoy and Gaimard, and was subsequently 

 reported as common on the coast of New South Wales. In study- 

 ing the collections accumulated by the German ship " Gazelle " I 

 found that the species of Ptilometra occurring at Dirk Hartog 

 Island was different from that occurring at Sydney, and I accord- 

 ingly called it Ptilometra dorcadis. Ic now became a question 

 whether this species or the one I considered for the time macro- 

 nema (the one occurring at Sydney) was the true macronema 



