124 .BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



areas, less than 4 mm. from the margin. Against it rest two columns 

 of supramarginal plates. 



The inframarginal plates, of which there are at least 45 in each 

 column, are distally small and subquadrate but proximally increase 

 rapidly in size and at the base of the columns are three to four times 

 as wide as long. These plates bear numerous pitted pustules upon 

 which articulated short, sharp, smooth spines. The columns of ad- 

 joining rays meet in the axils and continue into the interbrachial 

 areas. 



The adambulacral plates are like the inframarginals but do not 

 increase so rapidly in width as those plates and are somewhat more 

 numerous, there being in a complete ray about 52 in a column. 

 Proximally some of the large plates are broken into two or three 

 often very convex ossicles. In addition to the small spines like those 

 of the inframarginals, each plate bears on its ambulacral edge a prom- 

 inent socket in which articulated a long, thick, smooth spine. The 

 adambulacral plates in the proximal third of the rays each have a 

 small, more or less wedge-shaped, carinated, accessory adambulacral 

 plate. In this region these ossicles separate the adambulacrals from 

 the ambulacrals and beneath the accessory adambulacral plates are 

 the podial openings. Five or six adambulacral plates of each column 

 abut against the interbrachial marginal plates, while five or six pairs 

 continue orally, the terminating pieces being of the oral armature. 



Ambulacral furrows Vvide, increasing in ^\adth proximally. An 

 angular median sinus marlcs each ambulacral furrow. Ambulacral 

 plates short but wide, slightly overlapping proximally, and one to 

 each adambulacral plate. All of the plates are strongly carinated, 

 the carina in the distal two-thirds converging medially and proximally. 

 In the proximal third the carinas gradually are changed in form and 

 are there arranged in forked pairs. In other words, the carinas adjoin 

 the accessory adambulacrals, are arranged in pairs, continuing ad- 

 joining and straight for a short distance, and then diverge in broad 

 curves, terminating near the center of the ambulacral gToove. This 

 arrangement produces in the proximal portion of the ambulacral 

 furrows four columns of ovoid pits, all terminating laterally into 

 podial openings. Every other podial opening belongs to the same 

 column, one series beneath the adambulacrals, the other gradually 

 passing medially in the ambulacral grooves. In the distal two-thirds, 

 however, the podial openings are arranged in single columns, one to 

 each ambulacral plate and issuing from underneath the adambulacrals. 



Interbrachial areas with seven plates, each composed of two prox- 

 imal inframarginals, beneath which are two pairs of interbrachial 

 marginals and a single diamond-shaped axillary marginal plate. AU 

 bear similar spines and ornamentation on the inframarginals. Some- 

 times one of the distal interbrachial marginals may be divided and 



