NO. 5 CLARK : ECHINI OF WARMER EASTERN PACIFIC 229 



Order CIDAROIDA I 



Family Cidaridae 



Eucidaris Thouarsii (Valenciennes) 



Plate 35, Fig. 1 



Cidaris Thouarsii L. Agassiz and Desor, 1846, p. 326. 



Cidaris (Eucidaris) Thouarsii Doderlein, 1887, p. 20. 



Eucidaris Thouarsii Mortensen, 1928a, pp. 393-400, pi. 42, figs. 5-13. 



There are, in the Hancock collections, more than 1,200 specimens from 

 175 stations. They range in size from 3.5 to 67 mm in diameter. The 

 largest and finest specimens are from the Galapagos Islands, particularly 

 Darwin Bay, Tower Island, and Cartago Bay, Albemarle Island. The 

 character of the spines, both primary and secondary, shows extraordinary 

 diversity. The secondaries range from relatively short, truncate spines to 

 rather long ones tapering to a chisel-like tip. The primaries show even 

 greater diversity ranging from short, stout spines with diameter .25-.30 

 of length to slender terete spines with greatest diameter less than a tenth 

 of the length. There is great diversity also as to the extent to which the 

 spines are covered with sponges, bryozoa or calcareous algae. Occasionally 

 these foreign growths increase the diameter of the spine (at least at its 

 base) to one-third of its length. In other individuals of the same size, from 

 the same station, the spines may be entirely free from any foreign growth. 



The greater part of the Velero collection of Thouarsii is from the 

 Galapagos Islands and a notable proportion of these individuals are larger 

 and stouter than the material from the mainland coast. The specimens 

 from Colombia, Panama, Costa Rica, and Mexico are on the whole smaller 

 and have more slender spines than those from the islands. Occasional, 

 sometimes conspicuous, exceptions prevent the drawing of any clear line 

 ot distinction however. Mortensen's emphasis on the "nearly black" 

 secondary spines in galapagensis is misplaced as most specimens from either 

 mainland or islands have the secondaries a deep purplish brown, the shade 

 apparently deepening with age. On the whole, it seems to me futile to try 

 to maintain any well-defined form as a variety or subspecies galapagensis. 



Mortensen (1928, p. 399) has called attention to certain peculiarities 

 in a specimen from Clarion Island which, if constant, would warrant 

 recognition as at least a variety of Thouarsii. Unfortunately the present 

 collection contains only a very few specimens from Clarion Island. While 

 the largest of these seems to resemble the one studied by Mortensen, the 

 others are not distingin'shable satisfactorily from specimens from the main- 

 land coast. Further collecting at Clarion Island is greatly to be desired. 



Distribution. — This is one of the most characteristic sea-urchins of 

 the western coast of tropical and subtropical America. E. Thouarsii 

 occurs also at the outlying islands (Clarion, Socorro, Cocos and the 



