120 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



radial areas are small. The plates bear groups of rather slender 

 spinelets, and in the interradial areas usually a central appressed 

 spine, except on the plates adjacent to the adambulacrals, which bear 

 pectinate or pectinate-fasciculate peJicellariae with 6 to 10 pointed 

 jaws. 



Adambulacral armature similar to that of euryactis, but furrow 

 spines 7 or 8, the eighth being usually a shorter spine at the adoral 

 end of the series. Proximally there are 8 or 9 subambulacral spines, 

 slender, terete, blunt, much shorter than the furrow spines and in 

 2 longitudinal series ; distally, 10 or 12 similar but relatively a little 

 fchorter spinules in 2 series, with often the beginning of a third, on 

 the outer part of plate. 



The mouth plates do not seem to differ constantly from those of 

 euryactis. 



Madreporic body similar to that of euryactis, situated at middle 

 of r; striae numerous, rather fine, raidating from near center. 



Anatomical notes. — The only internal features that show a tangible 

 difference from those of euryactis are the Polian vesicles and intesti- 

 jial coecum. The latter is of the same general form, but smaller, while 

 the former has a larger distal portion with fewer coccal appendages. 

 It is not unlikely that the form varies greatly with the degree of 

 expansion of the bladderlike portion, and the size of course would 

 vary similarly. 



Type.— C^it. No. 30522, U.S.N.M. 



Type-locality.— Station 5326, off northern Luzon (lat. 18° 32' 35'' 

 N. ; long. 122° 01' E.), 230 fathoms, mud; bottom temperature. 

 55.4° F. 



Distrihution. — Known only from off northern Luzon. 



Specimens examined. — Seven ; 3 from type-locality, and 4 from the 

 following stations: 



Station 5325, vicinity of type-locality, 224 fathoms, green mud. 

 bottom temperature 53.2° F. ; 1 specimen. 



Station 5328, vicinity of type-locality, 150 fathoms, blue mud. bot- 

 tom temperature 53.2° F.; 1 specimen. 



Station 5329, vicinity of type-locality, 212 fathoms, blue mud, bot- 

 tom temperature 51.4° F. ; 2 specimens. 



Remarks. — This species resembles both P. euryactis hrevispinus 

 and P. tenuis. It differs from P. anchistus in having the actinal in- 

 feromarginal spines, and in having narrower rays, narrower paxillar 

 area, shorter paxillar spinelets, and a less extensive series of actinal 

 intermediate plates on the ray. It is perhaps a little farther removed 

 from P. euryactis than is P. anchistus, and it stands about midway 

 between euryactis and tenuis. If anchistus and lusonicus are re- 

 garded as varieties of euryactis, then it will be difficult to consider 

 tenuis more than a variety of luzonicus. The result would be the 



