NUDECHIXUS SCOTIOPREMXUS. 277 



that Gravieri may also be very near Lytechinus verrucHlalus and rufus, but if the 

 buccal membrane is really free from calcareous matter, the resemblance is not 

 significant. Unfortunately Koehler does not state what the condition of the 

 buccal membrane in Gravieri is, as regards plates, and it is only because he places 

 the species in Gymnechinus that it is inferred the buccal membrane is thin and 

 naked. None of the species are known from more than one or two locahties, 

 but all are from the Indo-Pacific region. 



So far as our present knowledge goes, the six species of Nudechinus may be 

 distinguished from each other as follows : — 



Primary spines not distinctly banded with violet or rose. 



Test green or yellowish green or light with green blotches; spines white or whit- 

 ish, green or brown at the very base scotiopremnus. 



Test and spines not as above. 



Secondary spines not swollen at tip; valves of tridentate pedicellariaj wide, 



not compressed at base of blade darnleyensis. 



Secondary spines somewhat swollen at tip; valves of tridentate pedicel- 



larise strongly compressed in basal part of blade inconspicuus. 



Primary spines distinctly banded with violet or rose. 



Test whitish blotched with deep violet; primary spines white, each with a broad 



band of rose-violet (K. & V. 597) slicius. 



Test and spines not as above. 



Test gray greenish with some deep green spots: primaries grayish white 



with 2 or 3 bands of clear rose Gravieri. 



Test variegated with white and light and dark green; primaries with 2 or 



3 violet bands near tip multicolor. 



Nudechinus scotiopremnus/ sp. nov. 

 Plate 97, figs. 4-6. 



The type-specimen (PI. 97, fig. 4) is 17 mm. in diameter and 10 mm. high; 

 the actinostome is 7 mm. in diameter while the abactinal system is only 3.5 mm. 

 and the periproct 1.5 mm. There are 18 interambulacral plates in each column 

 and 22 ambulacrals. The primary spines are about 3.5 mm. long at the ambitus. 

 In the largest specimen, the diameter is 21 mm., the height 13 mm., the actino- 

 stome 10 mm., the abactinal system 4.5 mm., the periproct, 2 mm., and the 

 primary spines about 4 mm.; there are 18 interambulacral, and 23 ambulacral 

 plates in each column. In the smallest specimen, the figures are, 13 mm. h. d. 

 9 mm. V. d.; 6 mm. actinostome, 3 mm. abactinal system; 1.33 mm. periproct; 

 2.5 mm., primary spines; 14 interambulacrals; 17 ambulacrals. 



1 cTKOTios = dark -f- Trptfxvov = the lowest part of the trunk of a tree, the base. 



