ASTEEOIDEA OF H.M.S. ' CHALLENGER ' EXPEDITION. 2l7 



spines whicli border tlie vertical furrows that run between the 

 consecutive marginal plates in Astropecten and other forms. 



As the structure is very constant and appears to form a reliable 

 specific character, useful in determination, I propose for tbe sake 

 of brevity to speak of it in the descriptions which follow under 

 the name of the " cribriform organ.^^ 



In species which have more than one of these organs in each 

 interbrachial angle, the additional ones occur on the vertical 

 sutures immediately succeeding on either side of the median line, 

 and are identical with the median organ just described. No 

 case of irregularity or intermission occurs in any of the specimens 

 I have examined. The number of cribriform organs present in 

 each angle appears to be always constant in a species ; and 

 species exist which possess 1, 3, 5, 7, 9, or even 14 of the organs 

 respectively. The organ varies in the different species as regards 

 its breadth, the number of vertical parallel lines or pseudo- 

 lamellse which compose it, and the character of the integral 

 calcareous bodies of which these latter are formed. In l^or- 

 cellanaster the component parts are strictly lamellar in form, as 

 described above ; whilst in the allied genera Hyphalaster, Styra- 

 caster, and Tlioracaster the corresponding elements are papil- 

 liform. 



PoECELLANASTEE, WyvUle TTiomson. 



Rays five, comparatively short, upturned at the extremities and fre- 

 quently reverted over the dorsal area. Disk more or less inflated. Supero- 

 marginal plates not united along the median line of the ray, usually bearing 

 a spine ; and these form a series on either side of the ray. Abactinal 

 area covered with membrane, beset M'holly or in limited areas with simple 

 spiniferous spicules. A more or less elongate tubular epiproctal prolon- 

 gation * is present in the centre of the disk, which may be equal in length 



* Prof. E. Perrier has recently published a note (Comptes Eendus, December 

 1882, p. 1379) on two small Starfishes obtained off the north coast of Spain, 

 from a depth of 1960 and 2650 metres respectively. A new genus has been 

 established for their reception, and named Ccmlaster, in reference to the dorsal 

 peduncle with which they are furnished. Both specimens are very small, the 

 larger of the two measuring only 6 millim. from the centre of the disk to the 

 extremity of a ray ; whilst in the smaller one the embi'yonic plating of the disk 

 is still present. The few striking characters briefly mentioned by M. Perrier 

 accord in every particular with Forcellanaster ; and, as far as I am able to judge 

 from the meagre information, I am constrained to regard these interesting 

 Starfishes as young forms of some species of that genus. As to their identity 

 with, or distinction from, the more western Atlantic species P. ccsruleus, Wy. T., 



