STARFISHES OF THE PHILIPPrNE SEAS. 189 



to truncate jaws (2 or 3 times thicker than the actinal spinelets) 

 confined to a single plate, or sometimes shared by 2 plates (in inter- 

 radial area). The pedicellariae are similar in form to those of P. 

 •filholi Perrier {^=forcipatus Sladen). 



Thirteen adambulacral plates (exceptionally 12 or 14) correspond 

 to first 10 inferomarginals. Furrow margin of plate semicircular, 

 about as salient as in numicus; consecutive plates separated by an 

 interval equal to about two-thirds or three-fourths the length of 

 the plate, at base of ray. Furrow spines in type, 8 at base of ray, 

 then 7, and on outer part of ray 9 or 10. It is difficult to determine 

 exactly the number of furrow spines, because on the transverse 

 margins of the plate are 1 to 3 spinules which partly or wholly form 

 a part of the palmate furrow^ series (especially distally where the 

 plates are narrow). There is 1 prominent tapering, sharp, some- 

 times slightly curved subambulacral spine about as long or a little 

 longer than the adjacent inferomarginal plate. Frequently, but 

 not always, near the above and the outer adoral corner of plate is 

 a small spinule distinct from the spinules of the transverse margin, 

 or rarely 2 or even 3 spinules may be present on a few proximal 

 plates. 



Marginal mouth spines, 6 or 7; about 7 spines along the median 

 suture, flattened, pointed, and decreasing in length toward outer 

 end of plate. On the surface of plate, near inner end, an inter- 

 mediate series of about 3 spines (in small specimens 1 or 2 only), 

 of which 1 is enlarged but is smaller than the homologous subambu- 

 lacral spine. 



Madreporic body situated about its own diameter (or a little more 

 or less) from inner edge of marginal plates; striae coarse. 



Anatomical notes. — The dorsal muscles are very stout and are 

 found on the outer part of the ray. The end of the ray is usually 

 recurved, and sometimes forms a spiral. The muscles of either side 

 are attached to the dorsal body wall and to the outer end of the 

 sixth or seventh ambulacral ossicle, w^hich differs from the rest in 

 being higher and having a special knoblike crest at the outer end 

 for the attachment of the tendon. This tendon, in spite of the size 

 of the muscle, is rather inconspicuous. The muscles are much 

 heavier and the tendon longer and decidedly less conspicuous than 

 in P. agassizi evoylus (from California) and P. filholi (from the 

 Atlantic). These two species are also relatives of P, mimicKs. The 

 difference in the muscles alone will distinguish hylacanthus from 

 ■filholi and evoplus. Not infrequently the muscles are so strongly 

 contracted that the^^ have entirely broken away from the tendon, 

 which will be found, however, attached to the ambulacral ossicle 

 (usually easily recognizable by its greater height) . 



