A MONOGRAPH OF THE EXISTING CRINOIDS 



175 



DECAMETRA ZEBRA (H. L. Clark) 



Oligometra zebra H. L. CLARK, Biol. Results Fishing Exper. F. I. S. Endeavour, 1909-14, vol. 4, 



pt. 1, 1916, p. 22 (detailed description; locality), pi. 2, fig. 2. 

 Decametra zebra H. L. CLARK, Echinoderm fauna of Australia, 1946, p. 52 (in key), p. 53 (notes; 



transferred to Decametra at suggestion of A. H. Clark). 



Diagnostic features. The cirri are 12-13 mm. in length with 27-28 segments, all 

 of which are broader than long; P! is nearly as long as P 2 ; PS is similar to P 2 , but a 

 little smaller; the aboral margins of the basal segments of P 2 are more or less pro- 

 duced as flattened spinulose projections; the arms are about 70 mm. long. 



Description. The centrodorsal is 3 mm. in diameter, with the dorsal pole 

 markedly concave. The cirri are arranged hi a single crowded fairly regular mar- 

 ginal row. 



The cirri are about XX, 27-28, from 12 to 13 mm. long. All of the component 

 segments are broader than long. The basal segments are nearly square, but distally 

 each successive segment becomes more compressed, ventrally rounded, and dorsally 

 transversely ridged. The transverse ridges are never conspicuous, but become more 

 evident on the last four segments, especially on the penultimate where the transverse 

 ridge forms a well marked opposing spine. 



The IBr scries are not peculiar, the synarthrial tubercles, however, being quite 

 distinct. The IBr 2 (axillaries) are nearly twice as broad as long. The adjacent 

 IBr series are well separated from each other. 



The 10 arms are about 70 mm. long. The brachials are at first quadrilateral, 

 later becoming triangular and then near the tip of the arm again quadrilateral. The 

 synarthrial tubercles are well marked. Neither the distal margins nor the distolateral 

 angles are peculiar, though the latter are evident enough, especially in the terminal 

 half of the arm. The general contour of the arms is quite smooth. 



P! is about 7 mm. long and is not at all rigid or otherwise peculiar. It consists 

 of 18 segments of which the basal six or seven are broader than long and those suc- 

 ceeding are about as long as broad, or a little longer than broad. The oral margins 

 of the lower segments are barely produced into one or two minute spines, while the 

 aboral margins are inconspicuous, flattened, and a trifle roughened. The eighth- 

 twelfth segments are somewhat prismatic, and the remaining segments are distinctly 

 flattened. P 2 is 9 mm. long with 18-20 segments. It is very similar to P t but is 

 obviously stouter, and is clearly the largest pinnule on the arm. The oral margins 

 of the basal segments are smooth, while the aboral margins are more or less produced 

 as flattened spinulose projections. The distal margins of all the segments except the 

 first five or six are finely spinulose. But none of these characteristics are at all 

 conspicuous. P 3 is much like P 2 , but it is a little smaller. P 4 , which is probably 

 the shortest pinnule on the arm, is only a trifle shorter than P 3 . The pinnules suc- 

 ceeding become very slender, from 8 to 9 mm. long with 22 or more segments. On 

 the basal half of the arm the pinnule segments, except for the basal two or three, 

 have distinctly, but finely, spinulose aboral edges and distal margins, but on the 

 outer half of the arm they seem to be quite smooth. 



In the dry type specimen the centrodorsal, the basal portion of the cirri, and 

 all the brachials and pinnules are uniformly pale buff or brownish white. The cirri 

 gradually become dull purple at the tip, the lighter color being confined more and 



