172 Proceedings of the Biological Society of Washington. 



the average) is much enlarged and hears a stout conical centra] spine 

 ahout 3 mm. long. 



The next row is not so regular as those preceding, and is composed of 

 slightly smaller paxilhe, which are more rounded ; many of them hear 

 spines like those in the preceding row. 



Within this fourth row the paxillre decrease rapidly in size and in reg- 

 ularity, so that the central third of the arm is occupied by small, irregular, 

 closely placed, though not crowded, rounded paxillae, many of which are 

 enlarged and bear a conical spine, especially in the outer part of the arm. 



On the disk the paxillse in the center, continuing thence along the 

 midradial region of the arms, are small and rounded ; toward the inter- 

 brachial arcs and the margins of the arms they rapidly become larger, 

 more oblong or quadrate, more spaced, and more regular in arrange- 

 ment. Only one or two of the paxillse on the disk bear spines, and these 

 spines are small ; on the arms the spines appear first along the sides, and 

 it is only in the outer half that they become as abundant in the median 

 as in the lateral areas. 



The inferomarginal plates bear three long stout spines, of which the 

 lowest, situated just below the ambitus, is the longest, 9 mm. in length; 

 the second, situated at the ambitus, is similar, but slightly shorter; the 

 third, situated on the abactinal surface, is the shortest, usually about 4 

 mm. long; on the actinal surface below the first spine in the preceding 

 series the inferomarginals bear from three to five spines of considerable 

 length, though much shorter than those in the upper series, which de- 

 crease in size toward the ambulacral groove; the sides of the inferomar- 

 ginals are bordered with very numerous capillary spinelets. 



The actinal intermediate plates have usually a single prominent median 

 spine; their proximal and distal borders bear numerous capillary spine- 

 lets. 



The adambulacral plates are slightly narrower than the actinal inter- 

 mediate plates, which in turn are slightly narrower than the inferomar- 

 ginals; they bear a sabre-shaped spine in the furrow, followed by a 

 similar, but longer, stouter and less curved spine, beyond which are two 

 slightly shorter straight spines, the distal the smaller; the inner half of 

 the plate is bare; the proximal and distal borders are fringed with num- 

 erous capillary spines. 



The mouth plates are narrow, with eleven gradually descreasing spines 

 situated along the median suture, and four similar spines situated along 

 the furrow margin ; the mouth spines proper may be said to consist of 

 the first spines in these two series ( the inner being the larger) and a third, 

 more or less widely spaced from these and making a considerable angle 

 with them, situated deep in the groove on the aboral edge of the plate; 

 the border adjoining the first adambulacral is fringed with capillary 

 spinelets. 



The color in alcohol is a very dark brown above, the crowns of the 

 paxilk-e white except for the bordering spinelets, which are dark brown ; 

 the enlarged spine-bearing paxillse and the abactinal surface of the infero- 

 marginals are deep brown ; the spines are white, except for those included 



