MUSEUM OF COMPARATIVE ZOOLOGY. 263 



cluster of three or four small tubercles ; the ocular plates are also pentago- 

 nal, elongated horizontally. The color of the test is greenish (in alcohol), 

 mottled with dark violet patches ; the spines are of the same greenish 

 tinge, banded irregularly with reddish, transverse bands.. In other speci- 

 mens we have the same pattern of coloration, in different shades of green, 

 with white spots irregularly scattered over the surface. 

 From 30 to 160 fathoms. 



Trigonocidaris albida A. Ao., nov. gen. et sp. 



This genus is allied to Genocidaris. The principal tubercles have the 

 same structure ; but, in addition, the whole test is covered by a reticulation 

 of ridges, similar to those of Podocidaris, extending from the base of the 

 different tubercles, both primary and secondary, and uniting them all in a 

 complicated, raised system of network, with irregularly shaped cells, the 

 ridges leaving more or less deep pits, giving the test the appearance of 

 having been gouged out in spots. The spines are long, slender, somewhat 

 transparent, longitudinally striated, with slight, transverse striation. The 

 abactinal system resembles that of Caenopedina, but the anal system is cov- 

 ered by only four triangular plates, one of which is much larger than the 

 others. Prom the fact that in the youngest specimens examined we find 

 them already, I am tempted to suppose they never increase in number, 

 and remain as they are, as in Echinocidaris. The actinal membrane is, as 

 in Lytechinus, entirely covered by a number of rather large plates irregu- 

 larly arranged, the ten buccal plates being but slightly larger than the 

 others. The actinal opening is of moderate size, slightly indented ; the 

 auricles are exceedingly slender, and disconnected at the extremity. 

 There are but two principal rows of primary tubercles, both in the ambu- 

 lacral and interambulacral zone, with from five to six minute tubercles 

 seated upon the connecting ridges in the latter zone, and two to three upon 

 each plate in the former. The poriferous zone is narrow ; the pores are 

 placed obliquely in an unbroken vertical zone, three to each ambulacral 

 plate, and separated by ridges running from the ambulacral tubercles to the 

 interambulacral zone, similar to those joining the tubercles. The test, as 

 well as the spines, are almost white, the latter having only a slight tinge of 

 yellow when largest. The whole test is covered with pedicellaria?, having a 

 sharp-pointed head articulated upon a long, slender thread, seeming scarcely 

 capable of supporting the head. 

 From 40 to 270 fathoms. 



