A MONOGRAPH OF THE EXISTING CRINOIDS 311 



on the west coast); p. 445 (summary of west Australian records); Memoirs Australian Mus., 

 vol. 4, 1911, p. 723 (Holothuria Bank; Baudin I.); p. 724 (peculiar to north Australia); p. 

 733 (in key); p. 741 (description; localities; relationships; arm division); Crinoids of the 

 Indian Ocean, 1912, p. 79 (references; locality); Smiths. Miscell. Coll., vol. 61, No. 15, 1913, 

 p. 8 (published references to specimens in the British Museum; localities); Internat. Revue 

 d. gesamt. Hydrobiol. u. Hydrogr., 1915, pp. J24 ami following (detailed account of the dis- 

 tribution in Australia). II. L. OI.AKK, Biol. Results Fishing Exper. F. I. S. Endeavour 

 1909-1914, vol. 4, pt. 1, 1916, p. 6 (characteristic of the west Australian subrcgion).- A. H. 

 CLARK, Unstalked Crinoids of the Siboga Exped., 191S, p. 275 (listed). H. L. CLARK, The 

 Echinoderm Fauna of Torres Strait, 1921, pp. 192 and following (range). 



Comatula cotalaria A. H. CLARK, Memoirs Australian Mus., vol. 4, 1911, p. 716 (typographical 

 error) . 



Comatula (Validid) rotalaria A. H. CLARK, Unstalked Crinoids of the Siboga Exped., 1918, p. 6 

 (supposed by P. H. Carpenter to be closely related to Aciinometra notata [Comatella stelligera] ); 

 p. 25 (in key; synonymy; station 273). 



Comatula (Validia) etheridgei A. H. CLARK, Unstalked Crinoids of the Siboga Exped., 1918, p. 

 25 (in key; references; station 273); p. 26, fig. 1. 



Comatula etheridgi GISLEN, Zool. Bidrag frau Uppsala, vol. 9, 1924, p. 20. 



Diagnostic features. This is the only comatulid with 20 (18-27) arms, no cirri, 

 and all the division series of 2 ossicles united by syzygy. It is also the only comatulid 

 in which in young individuals the IIBr series bear arms of different lengths, the 

 inner longer than the outer. 



Description. In fully developed individuals the centrodorsal is a thin flat plate 

 wholly devoid of cirri, pentagonal or more or less sharply stellate, the flat, or some- 

 times slightly concave, dorsal surface of which is flush with the surface of the radials. 



In young individuals the centrodorsal is small, thin discoidal, bearing a variable 

 number of cirri which gradually drop off with increasing size as the centrodorsal 

 slowly sinks within the radial ring. 



The cirri, occurring only in the young, are X-O, 12-18. Most of the segments 

 are longer than broad. The segments are smooth, without dorsal processes, but a 

 small opposing spine is present. The cirri are slender and weak. 



The radials are short and bandlike, in close lateral contact, forming a hollow 

 pentagon, the interior of which is occupied by the centrodorsal. The IBr, are very 

 short, about as long as, or commonly slightly shorter than, the radials, beyond which 

 they form a hollow pentagon. The IBr 2 (axillaries) are united to the IBri by syzygy. 

 They are low triangular, from two to three times as broad as long or even broader, 

 with the lateral angles slightly truncated and the short sides thus formed in contact. 



In young individuals the IBr, are longer than the radials and widely free laterally, 

 becoming gradually shorter and broader during growth until they come into close 

 lateral contact. The IBr 2 are nearly pentagonal in the young and are widely sepa- 

 rated, becoming gradually broader until their lateral borders, now reduced almost to 

 a point, come into contact. 



The IIBr series are 2(1 + 2), very short, in close contact interiorly and, in large 

 specimens, exteriorly also. The IIIBr series, if present, are 2 (1+2) and resemble the 

 IIBr series. 



The arms are usually 20 (from 18 to 27) in number, up to 165 mm. in length, and 

 consist of about 150 brachials, of which the first 5 or 6 are nearly oblong, the follow- 



