ASTEROIDEA 141 



their slightly larger groups of spinelets, low on the side of the ray. The abactinal aspect 

 resembles Koehler's figure of Cribraster sladeni (191 2, pi. 6, fig. 6) except that the 

 madreporite is smaller, a diflference f)f no great importance since there is variation in 

 the size of the madreporite in georgianus and aurorae. The furrow is narrow and the 

 podia strictly biserial. 



The body wall is reinforced by a tough muscular lining. Imbedded in the wall are 

 small, spaced independent ossicles, irregularly oblong, triangular or lozenge-shape — the 

 bases of the paxillae. They are narrower than the interspaces, and the papulae are fairly 

 large, not numerous, irregularly distributed and confined to the abactinal surface. Each 

 plate develops a subcylindrical pedicel or tabulum 0-48-0-55 mm. high, the convex top 

 of which carries 2-6 slender spinelets o-6-o-7 mm. long. The tabulum is higher than in 

 georgianus. The spinelets are slender-clavate rather than capitate, and the terminal 

 third is armed with short thorns, shorter, less spiculate, and much less numerous than 

 in aurorae of comparable size. What I interpret as the proximal inferomarginal plates 

 carry about 9 spinelets. 



The small actinal areas have longer spinelets (o-S-o-q mm.) essentially like the 

 abactinal in form. These plates usually carry 3 or 4 spinelets in a close group and the 

 groups are rather crowded together. 



All the spines are heavily sheathed and look like tapered pointed papillae, between 

 which the rugose skin can be seen, especially on actinal surface. Only when dry do the 

 spines themselves become visible and take their proper shape. The sheathed spinelet is 

 two or three times the diameter at base of the spinelet proper, whence the appearance of 

 conical papillae. 



The adambulacral armature is typically " cryasteroid "—either an oblique series of 3, 

 decreasing in size outward from the heavy spatulate furrow spinelet (on aboral side of 

 plate), or else a triangular group of 3 spines, the outer having moved aborally. Some- 

 times the outer spine is duplicated by a fourth, the two forming a longiseries. The furrow 

 spine is frequently scoop-shaped, and the second spine may also be compressed, or 

 spatulate. There are 4 heavy marginal mouth spines, also compressed, and about 2 



suborals. 



There is a prominent interbrachial septum, broader above than below, which does not 

 extend across the actinal interradial area but leaves a wide passage (filled with gonads). 

 It is heavily fortified with ossicles hidden by very tough tissue. The coarse-lobed ovaries 

 open interradially on side of ray above marginal plates. The ampullae are bilobed as in 

 typical " Cryaster". 



Koehler's photographs are much better than Perrier's. I have already alluded to 

 Koehler's figure of the abactinal aspect. The ventral surface (Koehler, 191 2, pi. 2, 

 fig. 12) is in poor condition but the figure shows the coarse flattened, furrow spines. It is 

 to be regretted that Koehler, a master of detailed description, did not give at least some 

 figures of spinelets. 



The Shag Rocks specimen is probably not typical since the type came from a faunally 



diflFerent area, the Falkland Plateau. 



