254 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



HISTOCIDARIS, species 



Plate 51, figs. 1,2; plate 77, figs. 5-8 



Locality. — Station 5664; Macassar Strait; Kapoposang Light bear- 

 ing N. 66° E., 3.8 miles distant (lat. 4° 43' 22" S., longfllS 53' IS" 

 E.); 731 meters; bottom temperature 6.28° C; hard bottom; Decem- 

 ber 28, 1909 (1 specimen, Cat. No. E. 1278, U.S.N.M.). 



Measurements 



Characters — The test is low, flattened above and below, with the 

 sides arched. The ambulacra (pi. 51, fig. 1) are 2.5 mm. wide, and thus 

 22.7 per cent of the interambulacra, which are 11 mm. broad at the 

 upper edge of the ambitus. The interporiferous zone is slightly wider 

 than the poriferous zone. The series of marginal tubercles is very- 

 regular ; the tubercles are rather small and not contiguous. The 

 median area is entirely naked, with scarcely a single small tubercle. 

 The pores are small, equal in size, and are separated by a distinctly 

 elevated wall. (Fig. 46.) 



The primary interambulacral tubercles are distinctly crenulate. 

 The areoles are not deep and are nearly circular, only the four lower 

 ones being confluent. The median area is half as wide as an areole; 

 the scrobicular ring of tubercles is rather prominent, the tubercles 

 filling almost the whole space so that there is hardly room for a few 

 small tubercles outside the scrobicular ring, and there is no naked 

 sunken median line. 



The apical system (fig. 8) is even more naked than usual in this 

 genus. Each genital plate carries 2 or 3 tubercles at the genital 

 pore and 2 or 3 rather large ones at the inner edge, the spines attached 

 to the latter being rather stout and together with those of the anal 

 system forming a dense cluster which closely covers the periproct. 

 The genital pores are already developed, though rather small, which 

 may mean either that it is a male specimen or that it is a female in 

 which the pores have not yet reached their full size. Each ocular 

 plate has 2 or 3 tubercles (spines) ; the ocular are all exsert. 



The peristome is still without interambularcral plates. 



The primary spines reach a length of at least 3 times the horizontal 

 diameter, the exact length being uncertain, as the points are broken 

 off. They are about 2 mm. wide at the base, and taper very slightly; 

 whether the point itself is broadened can not be ascertained. They 

 are provided with about 12 finely serrate longitudinal ridges, the 



