NO. 5 CLARK : ECHINI OF WARMER EASTERN PACIFIC 235 



Distribution. — Cocos Island, Galapagos. 



Ty/)^.— U.S.N.M. No. 27348. 



Type locality: — Albatross Station 3369, off Cocos Island, 52 fms. 



Depth.— A^-ZOQ fms. 



Specimens examined. — 1 specimen. 



Order GENTRECHINOIDA 



Family Gentrechinidae 



Centrechinus mexicanus (A. Agassiz)* 



Plate 38, Fig. 8 



Diadema mexicanum A. Agassiz, 1863, p. 20. 



Centrechinus mexicanus Ziesenhenne, 1937, p. 231. 



Diadema mexicanum Mortensen, 1940, p. 275, pi. 60, figs. 7-11. 



This big black sea-urchin, with long slender, acutely pointed and very 

 poisonous spines, is a nuisance to bathers, beachcombers and fishermen 

 throughout the tropical Eastern Pacific. Adult specimens are 70-80 mm 

 in diameter with the height of the test about half as much. The primary 

 spines may exceed twice the diameter of the test but they are so very fragile 

 that it is extremely difficult to preserve specimens with the spines unbroken. 

 The secondary spines are very slender and acicular but not very long; 

 when they dry they are so fragile they are easily broken and lost. The 

 absence of spines on the peristome is a constant and striking feature. Full 

 grown individuals are virtually unicolor, black or very dark brown; occa- 

 sionally definitely brown specimens occur. As in all the species of Centre- 

 chinus (or Diadema) very young specimens have the long spines prettily 

 banded with white and some dark shade, usually purple, but the white is 

 sometimes tinged with brown and the purple is nearly black. With increas- 

 ing size the white becomes more and more dingy and half grown specimens 

 may have it entirely suppressed and the spines all uniformly dark. Banded 

 spines in specimens half grown or more are common but usually only a few 

 of the primaries show it. The poisonous character of the spines is well 

 known and those who have once suffered the pain which even a single 

 spine can cause, are forever after extremely careful in the vicinity of 

 Centrechinus. 



Distribution. — This species was taken by the Velero at 38 stations, 

 of which the most northern was at Consag Rock in the Gulf of California, 

 the most southern at Gorgona Island, Colombia. The absence of specimens 

 from the western coast of Lower California is notable, since the urchin 

 occurs at both Socorro and Clarion Islands. It is also found at Cocos 

 Island and throughout the Galapagos Islands. It is definitely a shallow 

 water echinoid, for, although it was taken in 40-57 fms at the island, along 



*Please see explanation on p. 243. 



