106 Dr. W. B. Benham on an 



Above the chief row is a short imperfect and irregular row 

 of quite small tubercles (tertiaries) — about six at the ambitus 

 and below it, irregularly spaced, but rapidly diminishing 

 above to three, two, and one. The miliaries are not at all 

 well marked and are few in number. 



Ambulacrum. — Each ambulacral plate carries a single 

 primary situated immediately within the poriferous zone, 

 with two secondaries, of nearly the same size, forming a 

 transverse row on its mesial side. Below the ambitus the 

 second secondary soon disappears, and close to the actinostome 

 only the primary remains. 



Above the ambitus the reduction occurs at about the fifth or 

 sixth plate from the abactinal circle, while in the two upper- 

 most plates only the primary remains. 



Thus, while the interambulacral tubercles form distinctly 

 transverse rows, the ambulacrals form a vertical series, all 

 the tubercles being of nearly the same size. 



The poriferous zone is somewhat depressed, and this gives 

 the appearance to the narrow ambulacra of being raised 

 above the general level of the plates. 



(In a large specimen, 67 x 41 ram., the interambulacra are 

 very noticeably swollen, while the ambulacra appear as flat 

 depressions.) 



As Mortensen's diagnosis of the genus states, each ambu- 

 lacral plate bears three couples of pores, which are arranged 

 in a slightly zigzag line — the inner pore of the middle 

 couple being vertically below the outer pore of the upper 

 couple, while the outer pore of the lower couple is vertically 

 below the inner pore of the upper couple. 



The spines are short, the longest 5 mm. in length — fine, 

 pointed, grooved and coloured as described by Hutton 

 (though in other specimens they are uniformly white). 



In the apical ring the oculars are excluded from the peri- 

 proct ; the madreporite is prominent; the genital pores large; 

 and a row of secondary tubercles occurs near the apical 

 margin of each of these plates. 



The actinostome is nearly circular, the notches being very 

 slight, wide, and shallow. 



In addition to these two specimens which served for 

 Hutton's brief description, and one of which serves as type 

 of the new species, I have received several others, the largest 

 of which is 70 mm. by 50 mm. Some of them are paler 

 than the type, the spines being a dirty white, but all have 

 the tubercles pinkish orange. In the larger ones the number 

 of tubercles at ambitus is 9-10 in a transverse row, and the 



