230 DISCOVERY REPORTS 



adambulacral spines 2 (varying to i or 3), long, slender, terete, in a transverse series; 

 actinostome small, mostly occluded by the long teeth (a pair to each mouth angle); 

 furrows not wide; tube-feet slender, 4 ranked. 



Description. The convex abactinal wall is beset with widely spaced slender acicular 

 thorny spinelets (0-9-2 mm. long), the retracted sheath of which forms a soft collar at 

 the base and carries i or 2 to 5 or 6 characteristic crossed pedicellariae. The integument 

 is soft and until dried hides the skeleton. Between the spines are abundant papulae, 

 singly or in two's and three's, and here and there a lanceolate straight pedicellaria. In 

 alcoholic specimens the abactinal surface, under low magnification, has the appearance 

 of being covered with low papillae — a confused mixture of papulae, skin-covered 

 pedicellariae and spinelets. There is considerable difference between the two specimens 

 in the number of pedicellariae. In the smaller, most of the abactinal spinelets of ray 

 carry i or 2, and of the disk 2 or 3 ; whereas in the type the number is 5 or 6 for ray and 

 5-10 for disk. Madreporic body small (3 mm. diameter), situated at mid-r. 



On the side of the ray are two longiseries of acicular spines conspicuously larger than 

 the abactinal and surrounded by thick basal collars of crossed pedicellariae like the 

 abactinal. The upper or superomarginal are 2-2-25 mm. long by 0-35 mm. just above 

 base and carry 6-8 crossed pedicellariae, while the inferomarginal spines (sometimes 2 

 spines to a plate) are 2-9 mm. long by 0-5 mm. thick at base, and the fleshy sheath 

 carries upward of 25 crossed pedicellariae. The spines correspond to about every fourth 

 adambulacral plate and as the superomarginal plates are oriented obliquely to the 

 inferomarginals the superomarginal spine is usually above the interval between 

 2 inferomarginal spines. There is a series of single inconspicuous intermarginal papulae 

 which may represent encroachments of the abactinal system. 



Between the inferomarginal and outer adambulacral spine is a narrow zone of bare 

 skin devoid of papulae. The adambulacral spines are usually two in a transverse series on 

 the inner half of plate; often there are 3, or only i. They are long, slender (proximally 

 3-5 by 0-4 mm.), blunt, of nearly uniform diameter, and the proximal are a Httle longer 

 than the inferomarginals. The furrow face of the adambulacral plates carries numerous 

 small pedunculate straight pedicellariae of the common lanceolate form, 0-6-0-7 m"^- ^^ 

 length, and 0-35 mm. broad at base. 



The mouth-plates are small with a narrow actinostomial border, there being at each 

 mouth angle two long " teeth " extending over the peristome ; at outer end of each mouth 

 pair are two spines intermediate in size between the teeth and the first adambulacrals. 

 The narrow adoral carina, just back of mouth-plates, is composed of 5 or 6 pairs of 

 juxtaposed adambulacrals which generally carry only one spine each ; but sometimes a 

 second smaller one is present on the fourth to sixth. The mouth-plates carry an 

 abundance of small straight pedicellariae, exactly like the adambulacral. 



Phylogenetically the abactinal skeleton is degenerating. It is composed of very 

 numerous small plates forming a fantastically irregular reticulate structure, the irregu- 

 larly spaced nodes of which are formed by 3- or 4-lobed primary plates, bearing single 

 spinelets. The secondary plates are slender, overlapping, and the meshes are small, very 



