244 BULLETIN 76, UNITED STATES NATIONAL MUSEUM. 



KEY TO THE SPECIES OF BENTHOPECTEN HEREIN DESCRIBED. 



a- InfcromaiKinal plates with pectinate pedicellarise at base of ray only ; or if occurring beyond middle 

 ' of ray, actinal apinelets clavate (6-'). Odd interradial marginal plates normally present m all 



interradii. Actinal interradial areas small. ,. ,, . 



6' Abactinal plates of ray with only one slender central spinule; abactmal pedicellanae numerous 

 " on ray extending nearly to lip; actinal and inferomarginal spines of proximal part of ray not 



clavate- papulae often extending beyond eighth superomarginal acanthonolus, p. 144. 



6- Abactinal plates of rav proximallv with one spinule and several minute spmelets, beyond papular 

 area with one to several minute spinolets; proximally the actinal and inferomargmal spmes 

 clavate- abactinal pedicellaria> usually confined to disk and base of rays; papula; extending to 



fifth superomarginal claviger, p 150. 



a- A majority of interradii usually without odd intorradials, and inferomargmals with pedicellariae 

 nearly to tip of ray A few prominent spines in center of disk, the others short and stubby, robust. 

 Interradial areas larger mutabilu, p.m. 



BENTHOPECTEN ACANTHONOTUS Fisher. 



PI. 22, figs. 2, 3; pi. 23, figs. 1, 2; pi. 28, fig. 3; pi. 54, fig. 5; pi. 56, fig. 2. 



Benthopeclm acanthonotus Fisher, Bull. Bur. Fisheries for 1904, vol. 24, June 10, 1905, p. 299; 

 Zool. Anz., vol. 35, March 29, 1910, p. 547. 



Diagnosis.— R&ys five. R = 164 mm., r=14 mm., R = 11.7 r. Breadth of 

 ray at base, 16 mm. (from station 2919). Rays narrow, depressed, long, and very 

 gradually tapering to the attenuate extremity. Abactinal surface -with lobed 

 plates (on papular areas) bearing a single spinule, and also one to several very 

 small spinelcts. Pectinate pedicellaria^ numerous on abactinal surface, and extending 

 far along ray. Papular areas extensive; papulre extending as far as seventh to 

 t-wentieth superomarginal. Superomarginals -with one spine; infert)marginals -with 

 two; adambulacrals witli four to seven furrow spinelets and two much longer acti- 

 nals; mouth plates with four or five furrow and four or five actinal spines. Actuial 

 interradial areas small with one to three pectinate pedicellaria^. Inferomarginal 

 plates with pectinate pedicellariae at base of ray only. Superambulacral plates 

 absent, but each ambulacral with a fairly high thin dorsal ridge or carina, joined 

 tightly to marginal plate at its outer end. 



Desciiption. — Abactinal surface beset with rather widely spaced very slender 

 rugose or thorn-covered spinules; on ray one to a plate, but on disk usually accom- 

 panied by from one to six very small sjiinelets, sometimes forming a circle when 

 numerous. Spinules are largest on disk, being there unequal, however, and ranging 

 from about 1.5 mm. to 6 mm. in length; on rays they are about 1.5 mm. long. 

 Prunary abactinal plates, particularly the basals, have the longest spines. Abac- 

 tinal pedicellariae numerous, composed of two or three opposing series or combs 

 of three to six converging sharp spinelets. The apparatus is tisually circular in 

 form and from 0.75 to 1 .5 mm. in diameter, there being a total of nine to fifteen 

 spinelets, except far«along ray where the pedicellariae are beginning to form, and 

 have only four or five spinelets. Pedicellariae rather numerous on disk and more 

 so on ray, where they are found usually on either side of the median radial area, and 

 extend nearly to tip of arm. (See figure.) 



Abactinal plates wlien examined from inner surface are seen to be irregularly 

 lobed. In the type the plates are more delicate than in the other specimen. Plates 



