106 NATURAL HISTORY BULLETIN 



spines, 1 to 6 on a plate ; on the basal part of the spine itself ; 

 and on those dorsal plates that do not bear spines, 1 to 4 or more. 



On the interactinal plates they are variously placed and ir- 

 re^larly oriented; most of the plates have but one, which is 

 most commonly near the center, but many have two ; those plates 

 in the row next to the adambulacral plates usually have two or 

 three. The pedicellarise on the dorsal plates and on the spines 

 are smaller than those of the lower surface, but have the same 

 form and similar fossge. Each pedicellaria of the interactinal 

 and dorsal plates occupies a small, slightly elevated, smooth, 

 rounded or ovate area, surrounded by granules. A pedicellaria 

 and a stout blunt tubercle co-exist on some of the interactinal 

 plates, near the jaws. Many specimens are destitute of pedicel- 

 larise. 



Some specimens have large, stout spines on several of the in- 

 teractinal plates, near the jaws. 



The distal superomarginal plates of some large specimens bear 

 large, acute, conical spines. In other cases they bear lower ob- 

 tuse spines, or mere tubercles. The number of rows of large 

 radial spines is variable and also the number in a row. They 

 may be higher and more acute than in the type, and much fewer 

 in number. 



The number in the principal radial rows varies from three to 

 six, in the larger examples. Sometimes there are only eight to 

 ten large spines on the dorsal side, irregularly placed. 



I have examined four young specimens of this species from the 

 Blake Exp., preserved in the Museum of Comparative Zoology. 



Three of these were types of Pentagonaster parvus Perrier. 

 They agree perfectly with those of similar size collected by the 

 steamer Albatross in the West Indies. With the latter they 

 form a complete series, connecting the smallest with the full 

 grown examples from the same region. 



The specimens next to the smallest in size are 25 to 35™™ in 

 diameter (types of P. parvus) and usually have six marginal 

 plates on each side, above and below. In the smaller of these 

 the upper and lower marginal plates and the interactinal inter- 

 radial plates are nearly or quite covered with small granules, but 

 in the somewhat larger specimens more or less of the central area 

 of these plates is naked. Most of them show a distinct central 



