REPORT ON THE ECHINOIDEA— MORTENSEN 



273 



small miliary spines; still in this case it is rather different from what 

 obtains in Rhopalocidaris ; and besides, G. umbraculum has at least the 

 apical disks well developed. On the whole I think Rhopalocidaris a 

 very well delimited genus, the more so as all the species ( I have two 

 other species of the same genus from Japan) agree in the characters 

 pointed out as distinguishing the genus. 



RHOPALOCIDARIS HIRSUTISPINA, var. VIRIDIS.new variety 



Plate 61, fig. 2; plate 73, figs. 1, 2; plate 78, figs. 6-8 



Locality. — Station 5543; in the vicinity of northern Mindanao; 

 Tagolo Light bearing S. 75° W., 12.5 miles distant (lat. 8° 47' 15" 

 N., long. 123° 35' 00" E.); 296 meters; bottom temperature 12.50° C. ; 

 sand; August 20, 1909 (1 specimen, the type, Cat. No. E. 1382, 



U.S.N.M.). 



Measurements 



Description. — The test is rather high, flattened above but not 

 below; the sides are gently arched. The circumference is circular. 

 The ambulacra are scarcely at all sinuate. The interporiferous zone 

 is about twice the width of a pore zone. The marginal ambulacral 

 series of tubercles is quite regular; the tubercles are rather small, 

 but with a comparatively large, very distinct mamelon; they are not 

 contiguous, and generally there is a small miliary tubercle between 

 each two successive tubercles. Within the marginal tubercle there 

 is another almost equally large tubercle at the lower edge of the 

 plate, these inner tubercles thus alternating with the marginal ones. 

 They do not, however, occur regularly, some plates here and there 

 having only the marginal tubercle. The plates are otherwise entirely 

 naked and sunken, thus forming a very conspicuous sunken median 

 area, sharply delimited from the tuberculated part which forms like an 

 elevated ridge, being also rather sharply delimited from the poriferous 

 zone. The pores are equal sized, separated by a fairly broad and 

 somewhat elevated wall; the ridge between the pore pairs is rather 

 low. The whole pore zone is somewhat sunken. (PI. 73, figs. 1-2.) 



In the interambulacra the areoles are small, circular, even the low- 

 ermost ones being scarcely at all transverse-oval ; the 4 or 5 proximal 

 ones are confluent. The mamelon is relatively very large, the areole 

 correspondingly narrow and not very deep. The scrobicular ring is 

 rather inconspicuous; the scrobicular tubercles are not larger than 



