REPORT ON THE ASTEROIDEA. 489 



bulacral plates composed of transverse combs of spines united by web-tissue. It differs 

 from both genera in its transparent supradorsal membrane devoid of muscular fibrous 

 bauds, by the possession of three pairs of free secondary or superficial mouth- spines, arid 

 by its true pentagonal form. 



Chorology of the Genus Calyptraster. 

 «. Geographical distribution : — 



Atlantic : One species between the parallels of 0° and 15° S. 



Calyptraster coa, off the coast of Brazil, south-east of Per- 

 nambuco. 



/3. Bathy 'metrical range: Uncertain; between 32 and 400 fathoms. 



y. Nature of the Sea-bottom: Red mud. 



CJwrological Synopsis of the Species. 



1. Calyptraster coa, Sladen (PI. LXXVIII. figs. 1 and 2 ; PI. LXXIX. figs. 1-3). 



Calyptraster coa, Sladen, 1882, Journ. Linn. Soc. Lond. (Zool.), vol. xvi. p. 207. 



Marginal contour pentagonal, interbrachial arcs very slightly incurved. Minor radial 

 proportion 68 per cent. R= 11 mm. ; r= 7 5 mm. Abactinal surface flat, or even some- 

 what concave in consequence of the rays being slightly curved upward ; radial areas not 

 specialised externally, the supradorsal membrane forming a plane area. No marginal 

 fringe. Actinal surface convex. 



The supradorsal membrane is extremely thin and perfectly hyaline, a clean specimen 

 appearing to the eye as transparent as glass. No muscular bands are present, although a 

 fibrillar structure may be seen in the tissue under high magnification. The spiracula are 

 rather large, numerous, and uniformly distributed. The paxillse have long pedicles, and 

 are moderately delicate, evenly and equidistantly placed ; the crown is usually composed 

 of five spinelets, which are short in comparison with the pedicle, and rather delicate. A 

 few of the spinelets taper a little at their extremity, but usually they are slightly flaring. 



(zool. chall. exp.— part li. — 1888.) 62 



