190 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Variations. — The most important variation in this species is in 

 the occurrence of pedicellariae, which in the southern specimens are 

 more numerous than in the northern. They may be almost or entirely 

 absent (specimens from station 5445) or present on the actinal inter- 

 mediate plates, and intermarginally (the type) , or present interradi- 

 ally and on the actinal surface of the inferomarginals (station 5619). 

 The small spinelets of the abactinal plates may sometimes form 

 2 concentric series around the central spine, the inner series, how- 

 ever, usually incomplete (station 5629). 



Young specimens have few papular pores and few pedicellariae 

 (when these are present in the adults from the same station). The 

 relation of 10 inferomarginals to 13 adambulacrals is, however, 

 maintained. The abactinal spines are present all over the abactinal 

 surface in the smallest example examined (R=15 mm.). 



Type.— C^t. No. 32626, U.S.N.M. 



Type-locality. — Station 5467, Lagonoy Gulf, southeastern Luzon, 

 480 fathoms, green mud ; 1 specimen. 



Distrihution. — Molucca Passage to north coast of Samar, 383 to 

 435 fathoms, green mud, fine gray sand; bottom temperature, 44.3° F. 



Specimens examined. — Thirty-four. 



Station 5444, north coast of Samar (lat. 12° 43' 51" N.; long. 

 124° 58' 50'' E.), 308 fathoms, green mud, bottom temperature 45.3° 

 F. ; 1 specimen. 



Station 5445, north coast of Samar (lat. 12° 44' 42" N.; long. 124° 

 59' 50" E.), 383 fathoms, green mud, sand, bottom temperature 

 44.3° F. ; 19 specimens. 



Station 5619, Molucca Passage (lat. 0° 35' N. ; long. 127° 14' 40" 

 E.), 435 fathoms, fine gray sand; 13 specimens. 



Remarks. — As indicated in the diagnosis this species closely re- 

 sembles P. mi/nicus, from which it diifers in having only 13 adam- 

 bulacrals to the first 10 inferomarginals, while mimicus has 15 to 18. 

 In mimicus the abactinal spines are absent from the lateral portions 

 of the area, while in hylacanthus they are distributed all over the 

 area. 



P. mimicus inhabits depths of from 692 to 1,092 fathoms, sub- 

 jected to a temperature of 36.3° to 39.5°, while hylacanthus is found 

 in less than 500 fathoms, the only temperature record being 44.3°. 



P. hylacanthus resembles very closely Ch. niasicus., the two occur- 

 ring together at stations 5445 and 5619. The differences are pointed 

 out under the latter species. 



Genus CHEIRASTER Studer. 

 Cheiraster Studeb, 1883, p. 129 ; 1884, p. 49. Type, C. gazellae Studer. 



KEY TO THE SPECIES OF CHEIRASTER HEREIN DESCRIBED. 



o.^ Some of the abactinal plates of either rays or disk, or both, with enlarged 

 central spine at least 3 times ns long as the peripheral spinelets. 



