174 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.2 



distinctly but very slightly depressed, about 2 mm. long by 1 mm. 

 wide; there are 9 or 10 pore-pairs on each side with an insignificant 

 interporiferous area. Petals II and IV, not quite so depressed as I and 

 V but much larger, nearly 4 mm. long and more than a millimeter 

 wide; they extend outward at almost right angles to the long axis of 

 the test. Peripetalous fasciole rather wide but not very conspicuous on 

 the bare test as the minute spinelets which compose it are not very 

 densely crowded. Periproct on the sloping upper end of the test, rela- 

 tively large and entirely visible from above. It is a broad, pointed oval, 

 nearly as wide as long, with the largest covering plates in the upper 

 angle, the smallest around the anus near the lower margin of the area. 

 Subanal plastron large, about 6 mm. across, nearly circular but some- 

 what pointed where in contact with the sternum; the enclosing fasciole 

 is evident but not at all densely spinulose ; near the periproct the fasciole 

 is somewhat diffuse but there are no definite anal branches. Sternum 

 very small, triangular, about 5 mm. long by 3 wide, almost completely 

 covered with tubercles. Peristome approximately circular, 2 mm. across, 

 with the mouth at center, covered with delicate but relatively large, 

 angular plates; most of these plates cany each, a single spine; on the 

 plates close to the mouth these spines are short and thick, elsewhere 

 they are long and slender, similar to those of the test but much smaller ; 

 the mouth itself is not quite 5 mm. from the anterior end of the test. 



Under a magnification of 95 diameters, several sphaeridia are notice- 

 able on the oral portion of each ambulacrum, except III which appar- 

 ently lacks them. Spines cover practically all parts of the test but are 

 smallest and most scattered on the ventral ambulacra. They are largest 

 and longest on the most elevated parts of the interambulacra 2 and 3, 

 on the sternum and especially on the posterior portion of the test where 

 many are 3-5 mm. long. They are delicate, more or less curved and 

 usually somewhat tapering and pointed, but not a few are distinctly 

 thickened at the tip. No pedicellariae were detected with a hand lens 

 but prolonged search with a magnification of 95 diameters revealed 4 

 thick-headed tridentate pedicellariae in ambulacrum V. These are not 

 essentially different from those of Hemiaster; the heads are .25 mm. 



