ASTEROIDEA 189 



elevated. As the internal organs are badly macerated, it may well be that the body form 

 is not at all what it would be in life. 



I have figured (Fisher, 1911, pi. 115, fig. 5) the abactinal skeleton of P. biserialis. It 

 seems obvious from an examination of a prepared sample of the large specimen that 

 there is no fundamental diff'erence between the two species. In folliculatus an increase in 

 the number of cruciform primary plates does not keep pace with increase in size of the 

 animal. As a consequence the tufts of spines become widely spaced and the skeletal 

 intervals greatly enlarged. The slender, secondary, spineless ossicles lengthen and, instead 

 of I, 2 or 3 connect the nodal points of the skeletal net. The character of the spinelets is 

 similar in the two species, 4 or 5 being a common number for each abactinal fascicle. In 

 the large specimen the papulae are much more numerous, and more conspicuous on 

 account of the spacing of the fascicles of spines. In the small specimen (in which the 

 skeletal net has smaller meshes than in P. biserialis) the papulae per area range from i to 

 5, but in the large specimen there are commonly 8-12. 



The madreporite is very large, with an irregularly lobed contour ; extreme diameters 

 17 and 19 mm. 



Sladen gives good figures of the actinal surface and description of the actinal armature. 

 He could not determine, without mutilating the type and only specimen, how many 

 spines belong to the adambulacral plates. I have made preparations of portions of the 

 actinal surface of both Falkland specimens. The "behaviour" of the plates is highly 

 peculiar. 



Small specimen. The lateral-most series of fascicles (each with 3 spines) represents 

 the superomarginals. Between each superomarginal fascicle and the furrow is a trans- 

 verse series of 5 slender acicular spines encased in a thick sheath as shown in Sladen's 

 fig. y, pi. 73. The sixth or outer "spine" in his figure is really the superomarginal 

 fascicle. The next spine toward furrow is the single inferomarginal, and the other 4 are 

 adambulacral. A sodium hypochlorite preparation cleared in glycerin shows that the 

 superomarginal plate, which is roughly oval in shape, is ankylosed to the dorsal and 

 distal face of the outer third of the adambulacral plate. Owing to difference of refraction 

 the two plates are easily identified. The inferomarginal can even be separated from the 

 adambulacral but at this stage ankylosis has actually taken place. The lobed supero- 

 marginals overlap the inferomarginal ossicle. 



Large specimen. Ankylosis of inferomarginal and adambulacral is complete. At the 

 outer end of the adambulacral, the inferomarginal portion bends slightly distad. The 

 angle is more marked on the dorsal aspect. On this side, the faint outline of the inner 

 portion of the inferomarginal can sometimes be discerned overlying the outer half of the 

 adambulacral, on its distal side, as in the small specimen. On the proximal two-thirds of 

 ray the superomarginals (with 3-5 spines), are widely separated from the inferomarginals, 

 the integument being devoid of any connecting skeletal elements. In middle of ray this 

 zone is 5 mm. wide. 



The adambulacral plates carry i or 2 short acicular furrow spines, and then a trans- 

 verse series of 5 slender acicular subambulacrals graduated in length from the inner 



