ECHINODEEMATA. 149 



belong to an outer, and at others to an inner circle on the disk ; and 

 that the colour which in some cases is light brown, in others is 

 purplish grey. 



Albany Island ; Torres Straits. 



Quite recently an example of this species has been received from 

 Kurrachee. 



8. Thyone mirabilis (?). 

 Thyone mirabilis, Imdwig, Semper's Arheiten, ii. p. 93. 



The form of the spicules would perhaps allow us to place the 

 single specimen here with doubt referred to this species either with 

 it or with Holoihwria dietriehii of Ludwig, the supporting-rods in 

 the suckers of the latter not being figured. Though bur specimen 

 has much more the form and colour, so far as one may judge froni 

 the description, of the Holothurian, the eight large arborescent and 

 two small tentacles, the scattered sucker-feet, and the unarmed 

 anal oriflc exactly determine its generic affinities. 



Port Denison. 



9. Thyone sacellus *. 



Stolua sacellus, Selenka, Zdt. f. wiss. Zool. xvii. p. 355. 



Thyone rigida, Semper, Holothurien, p. 66. 



Thyone sacella, von Marenzeller, Verh. «.-bot. Oes. Wien, 1881, p. 134. 



Torres Straits. 



10. Thyone okeni. (Plate IX. fig. D.) 



The two specimens of this spfecies are in remarkably good condi- 

 tion for examination, as one died with its tentacles fuUy expanded 

 and the other was laid open by the collector. > 



With the exception of the terminal plate in the suckers I have 

 not been able to detect any calcareous bodies either in the suckers 

 or the integument ; and if any such are present they must be ex- 

 ceedingly small and very rare. This characteristic brings this 

 species into proximity to the T. villosa of Semper, where, as in this, 

 the suckers are very closely packed. 



Elongated in form, very dark brown in colour (in spirit), tentacles 

 of about the same shade; suckers closely packed and distributed over 

 the whole body, their radial arrangement in the region of the anus 

 very obscurely indicated. Anus without teeth. Eetractors inserted 

 very nearly as far back as the middle of the body. Calcareous ring 

 of ten pieces, the radial similar to the interradial, elongated, and 

 wider below than above (fig. D). Calcareous plating extends some 

 way along the enteric tract (fig. D). Genital tubes numerous, very 

 slender and long, inserted behind the middle point of the length of 



* Prof. Selenta has been kind enough to inform me that Sacellus, as used 

 by him, Is a diminutive form of saccus, not of sacer. 



