154 Proceedings of the Biological Society of Washington. 



The superomarginals are narrow, their ridges being about as wide as 

 the deep channels between them ; the armature differs on alternate plates, 

 as follows: (1) just beneath the supermarginal paxilla there is a long 

 prominent spine 5 mm. in length, directed outward and obliquely upward ; 

 just below the ambitus there is a slightly smaller spine, directed outward 

 and slightly downward ; halfway between this and the actinal border of 

 the plate there is a much smaller, though similar, spine; (2) slightly 

 above the ambitus there is a long spine directed outward and very slightly 

 upward ; slightly below the ambitus there is a similar, usually very slightly 

 smaller, spine, directed outward and slightly downward; otherwise the 

 plate is as in the preceding type. At the base of the arm each infero- 

 marginal bears on its actinal surface from one to five (usually two or three) 

 pedicellarise, which vary all the way from granuliform to forcipiform, but 

 these soon disappear ; there are a few scattered spinules on the outer 

 surface, and the sides are abundantly supplied with capilliform spinelets. 

 The two inferomarginals in the center of the interbrachial arc bear 

 numerous short spines and spinules, or several conspicuous pedicellarise 

 and spinules. 



The alternation of two and three long spines on the inferomarginals, 

 and especially the occurrence of long spines just below the superomarginal 

 paxillse only on alternate plates, is a striking feature of the species. 



The actinal intermediate plates are narrow, with a knife-like crest 

 which bears a large and prominent pedicellaria of the forcipiform type 

 with usually one or two fine spinules near it. 



The adambulacral plates bear just within the furrow a sabre-shaped 

 flattened spine; just beyond this there is a much longer and stouter spine, 

 curved at the base; just behind this, so close to it as to arise almost from 

 a common base, there is a shorter straight spine. These spines are situ- 

 ated slightly beyond the median line of the plate, and proximal (adoral) 

 to them are usually from one to four slender spinules situated toward the 

 outer edge of the plate. 



The mouth plates have a long stout spine at the inner angle which 

 stands at the head of a series of seven spines arranged along the median 

 suture; these decrease gradually in length for the first four; the remainder 

 are much smaller ; on each pair of mouth plates, below and more or less 

 to one side of one of the spines of the central pair there is a large forcipi- 

 form pedicellaria; on the side opposite to that on which this pedicellaria 

 occurs there are two spines of rapidly decreasing length ; these spines, 

 with the median, stand almost in a straight line across the inner end of 

 the pair of mouth plates; at right angles to them, along the sides of the 

 individual plates, is a series of three slender spines, and along the side 

 bordering the first adambulacral many capillary spinelets. 



The color, in alcohol, is yellowish white. 



Type— Cat. No. 36,947, U.S.N.M., from "Albatross" Station 2787, 

 off the coast of Chile, in 61 fathoms. 



I take great pleasure in naming this species for my friend Dr. Carlos 

 Porter of Santiago de Chile. 



