238 bulletin: museum of comparative zoology. 



two species hitherto known by the coloration, which is pale buff above when dry, 

 more or less tinged witli purple when wet, becoming buffy-white beneath. The 

 sides of the bare interambulacral areas on the abactinal surface are more or less 

 distinctly yellow ; in many specimens the ambulacral edge of this area is marked 

 by a broad, dull red line extending from the ambitus to the genital plate, but these 

 lines may be interrupted and in about half the specimens are entirely wanting. 

 On the actinal side, some individuals have a deep brown line forming a more or 

 less perfect pentagon around the actinostome, about one-third of the distance to 

 the ambitus. The primary radioles are slender, of moderate but variable length, 

 the longest equalling the diameter of the test, and are decidedly flattened. They 

 are nearly white, but many have a purplish longitudinal stripe on the abactinal 

 side, and not infrequently they are handsomely banded with purple. There is no 

 blue anywhere on test or spines. The tuberculation of the test is more like that 

 of granulosum than of japonicum, but there are only eight series of primary inter- 

 ambulacral tubercles at the ambitus even in the largest individuals. The speci- 

 mens range in diameter from 42 to 70 mm. The test is very flat, the height 

 being only .25-. 30 of the diameter. The abactinal system is .30-.42 and the 

 actinal only .17— .24 of the diameter, while the anal system is .60-.65 of the abac- 

 tinal. The test is relatively higher and the abactinal and actinal systems larger in 

 small than in large individuals. 



Station 3856. Pailolo Channel, between Maui and Molokai, 127 fathoms. 



" 3857. Pailolo Channel, between Maui and Molokai, 127-128 fathoms. 



" 3957. Vicinity of Laysan Island, 173-220 fathoms. 



" 4103. Pailolo Channel, between Maui and Molokai, 132-141 fathoms. 



" 4104. Pailolo Channel, between Maui and Molokai, 123-141 fathoms. 

 Eighty-two specimens. 



Leptodiadema A. Ag. and Clark. 



This genus is established for a very small Diadematoid, which is apparently 

 quite different from any known genus. The size, form, and spines remind one of 

 Lissodiadema and the abactinal system is not altogether unlike that genus, but 

 the tuberculation is entirely different. Test flattened, both abactinally and actin- 

 ally. Ambulacra narrow, with pores in single straight series, not becoming 

 crowded at actinostome. Each ambulacrum carries a double series of primary 

 tubercles, extending from abactinal system to actinostome. Coronal plates 

 numerous (13-14 in specimen 9 mm. in diameter), each with a large primary 

 tubercle, at outer end. Below the ambitus, these tubercles are increasingly 

 nearer centre of plate, so that the two series of them converge and meet in a 

 point at actinostome. Beginning with the fifth (from abactinal system), each 

 coronal plate carries a second somewhat smaller tubercle, at inner end, and these 

 two series terminate about four plates from actiuostome. Secondary spines few ; 

 miliaries almost wanting. Primary tubercles, low, perforate, apparently finely 

 crenulate, those of the ambulacra smaller than those of the interambulacra. Ab- 

 actinal system moderate, with oculars on each side of madreporic plate excluded 



