PART 5 A MONOGRAPH OF THE EXISTING CRIXOIDS 101 



When viewed at right angles to the plane of their dorsal surface the IBr[ appear 

 oblong, about four times as broad as long; when viewed at right angles to the dorso- 

 ventral axis of the animal the median length appears to be about one third less than 

 the lateral; IBr 2 (axillaries) rhombic, half again as broad as long, the Anterior angle 

 sharp, the posterior process very broad and obtuse; the anterior borders are moderately 

 concave; the proximal borders are straight except just before they reach the lateral 

 border, where they turn to a horizontal direction and then curve slightly downward, 

 fitting snugly around the rounded distal angles of the IBr t ; the elements of the IBr 

 series and the first two brachials are in very close lateral apposition, and are more or 

 less sharply flattened against their neighbors. 



Arms 10, 100 mm. long; first brachial wedge-shaped, three times as long exteriorly 

 as interiorly, the inner border in close contact with that of its fellow; second brachial 

 nearly of the same size and shape, slightly larger and more irregular; first syzygial pair 

 (composed of the third and fourth brachials) slightly longer interiorly than exteriorly, 

 twice as broad as long; following brachials as far as the second syzygy irregularly 

 wedge-shaped, about three times as broad as long, those beyond the second syzygy 

 triangular, somewhat broader than long, soon becoming wedge-shaped, slightly broader 

 than long, and distally wedge-shaped, about as long as broad, and terminally longer 

 than broad. 



Syzygies occur between brachials 3+4, 9 + 10, 14 + 15 and distally at intervals of 

 three muscular articulations. 



P! is 7.5 mm. long, composed of 10+ segments, of which the first is twice as broad 

 as long, the second is slightly longer than broad, the third is half again as long as broad, 

 and the following are twice as long as broad, becoming three times as long as broad 

 distally; the third and following have rather prominent distal ends armed with fine 

 spines, at first only on the distal border (away from the ventral surface), later all 

 around; the pinnule is markedly stouter than those succeeding, and somewhat stiffened; 

 P 2 is 6 mm. long, with 10 segments, resembling P! but more slender and with propor- 

 tionately longer segments distally; P 3 is 4.5 mm. long, with 11 segments, smaller, more 

 delicate and less stiffened than P 2 ; distal pinnules from S to 9 mm. long and very 

 delicate, with 20 or 21 segments. 



Locality. Tahiti, Society Islands [A. H. Clark, 1918] (2, Munich M.). 



ECANTEDON PAUCICIRRA H. L. Clark 



Euantedon paucicirra H. L. CLARK, Rec. South Australian Mus., vol. 3, No. 4, 1928, pp. 369-370 

 (description; locality); fig. 109, p. 370. COTTON and GODFREY, Rcc. South Australian Mn-., 

 vol. 7, 1942, p. 232 (distribution). H. L. CLARK, Echinoderm fauna of Australia, 1946, p. 61 

 (size and color). 



Diagnostic features. Cirri XXV, 17-26 (usually about 20), the longest segment-; 

 about twice as long as broad; arms about 40 mm. long in the holotype. 



Description. The centrodorsal is low, hemispherical, about 2.5 mm. in diameter 

 and slightly convex, with the cirrus sockets closely crowded, arranged roughly in two or 

 three irregularly horizontal series. Cirri XXV, 17-26 (usually about 20), 10 mm. in 

 length ; the three basal segments are broader than long but the rest are longer than broad, 

 the sixth to tenth being the longest and up to twice as long as their median thickness. In 

 profile all but the first and last few segments are concave on the dorsal side and less so 

 on the ventral. The distal margin of the longer segments is oblique, the ventral side 



