214 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



CENTROCIDARIS. 



Centrocidaris A. Agassiz, 1904, Pan. Deep Sea Ech., p. 32. 



Test very flat, vertical diameter generally less than .50 h. d. ; coronal plates 7 or 8 ; 

 areolae very little sunken ; median interambulacral areas narrow, a little sunken, 

 and bare; ambulacra very broad, .55-.60 of interambulacra ; poriferous zones little 

 or not at all sunken ; median ambulacral area broad, flat, or somewhat depressed, 

 with a double marginal series of tubercles, outer much larger; intervening space 

 bare, or each ambulacral plate may carry an additional miliary tubercle; pores 

 very large, nearly or quite horizontal ; distance between two about equal to diam- 

 eter of pore; surface of interval slightly elevated. Abactinal system moderate, 

 .45-.50 h. d., with few (about 100) tubercles ; genital plates much higher than wide, 

 narrow, and bluntly-pointed externally; oculars entirely excluded from anal sys- 

 tem, very wide and low but sharply pointed, with a markedly concave outer 

 margin. Actinostome, .40-.45 h. d. Primary spines straight, cylindrical, slender, 

 and nearly or quite smooth, about equal to h. d. or somewhat longer; actinal prima- 

 ries not peculiar save for a wide collar ; secondaries flat, thin, and narrow. All 

 three kinds of pedicellariae usually present ; large globiferous ones of two quite 

 distinct sorts, one with broad, flat valves and neither lip nor end-tooth, the other 

 with curved valves (like Cidaris), but with a prominent end-tooth and lip. 



This monotypic genus was established for a very interesting and handsome 

 cidaroid taken by the " Albatross " in 1391 off Cocos Island, 52 fths. In 1904- 

 05, the " Albatross " obtained a dozen additional specimens near Hood Island, 

 Galapagos, 100-300 fths., so that it is now possible to diagnose the genus fully. 

 It is quite distinct from Goniocidaris, though it resembles it in the broad ambu- 

 lacra, but it is doubtful if it is nearer to any other known genus. 



Centrocidaris doederleini. 



Goniocidaris Doederleini A. Agassiz, 1898, Bull. M. C. Z., 32, 5, p. 73. 

 Centrocidaris Doederleini A. Agassiz, 1904, Pan. Deep Sea Ech., p. 33. 



Plate 14, figs. 1, 2, Pan. Deep Sea Ech., A. Agassiz, 1904. 



In young specimens the primary spines are very white and shining, and have 

 8-10 slightly elevated, glassy, longitudinal ridges, but these practically disappear 

 with age and the spines become dull and yellowish. In alcoholic specimens the 

 secondaries are green, slightly tipped with dark yellow, while the test is greenish 

 with the lines between the genital and ocular plates and the bare spaces of ambu- 

 lacra and interambulacra deep purplish or dull red. The largest specimen is 28 

 mm. h. d. and the longest spines measure 33 mm. 



APOROCIDARIS. 



Aporocidaris A. Agassiz and Clark, 1907, Haw. Pac. Ech. Cid., p. 36. 



Test flattened, .50-60 h.d. (but abactinal system sometimes so much elevated 

 that vertical diameter from centre of anal system, .60-. 80 h.d.), rather thin and 

 fragile; coronal plates 6, rarely 7; areolae only slightly sunken; median interam- 



