210 BULLETIN lOO, UNITED STATES NATIONAL MUSEUM. 



verse series. Nineteen or 20 plates correspond to the first 10 in- 

 feromarginals. 



Mouth plates with 5 to 8 furrow spines, the inner much enlarged, 

 the second slightly less so. Suboral spines 3 to 5. 



Madreporic body convex, prominent, touching an odd superomargi- 

 nal ; striae radiating ; ridges rather fine. 



Variations and young. — In specimens of the same size as the type 

 and cotype variation is found in the number of abactinal pedicellariae 

 of the rays; in the occasional presence of 1 or 2 minute spinelets 

 in addition to the regular spine of the abactinal plates ; in the num- 

 ber of inferomarginal pedicellariae; presence of actinal interradial 

 pedicellariae; in the number of oral spines (5 or 6 in type, 8 in 

 cotype) ; in the number of suboral spines (3 in type, 5 in cotype) ; 

 length of odd interradial superomarginal spine (7 or 8 mm. in type, 

 10 mm. in cotype). 



Small examples (R==30mm.) have relatively very prominent inter- 

 radial superomarginal spines, laclc abactinal pedicellariae on rays, 

 have very small or no accessory superomarginal spinules, have as 

 few as 4 or 5 furrow spines, 4 oral spines, and 3 suboral spines. 

 Specimens of intermediate size have 6 or 7 furrow spines, but the 

 number of oral and suboral spines varies in specimens of the same 

 size just as in the adult. The same is true of the actinal intermediate 

 pedicellariae. 



There is a very young specimen from station 5619, having R 9 mm. 

 The odd interradial superomarginal spines are 5 mm. long; furrow 

 spines 4 or 5, oral spines 6; no pedicellariae. 



Type.— Cat No. 32629, U.S.N.M. 



Type-locality. —Station 5618, Molucca Passage (lat. 0= 37' N.; 

 long. 127° 15' E.), 417 fathoms, gray mud; 2 specimens. 



Distribution. — Known only from Molucca Passage. 



/Specimens examined. — Nine ; in addition to the type, 7 from station 

 5619, Molucca Passage, near type-locality, 435 fathoms, fine gray 

 sand and mud. 



Remarhy,. — This species differs from B. huddlestonii Alcock in 

 having abactinal pedicellariae, only 2 inferomarginal spines, 2 sub- 

 ambulacral spines, and a less complete series of inferomarginal 

 pedicellariae. Although the type of moluccanus is much smaller 

 than that of B. huddlestonii.^ there are as many, or even 1 more, 

 furrow spines. In Ludwig's key to the species of Benthopecten (1910 

 p. 465) B. moluccanus would occupy a position just after B. huddle- 

 stonii, with a coordinate subhead reading: inferomarginal plates 

 with 2 spines: adambulacral plates with 7 to 9 furrow and 2 sub- 

 ambulacral spines; mouth plates with 5 to 8 oral spines. 



B. moluccanus differs from B. semisquamatus (Sladen) and B. ant- 

 arcticus (Sladen) in having pedicellariae and more numerous fur« 



