294 Yerrill, Notes on Radiata. 



Order, ECHINOIDEA. 

 In the identification of several species of the following Echini I 

 have been greatly aided by Mr. Alexander Agassiz, of the Museum 

 of Comparative Zoology, who kindly compared. with me a set of our 

 specimens with the types of species described by himself in the Bulle- 

 tin of the Museum, and also gave in exchange authentic specimens 

 of several of those species. Without this assistance some of the iden- 

 tifications could not have been made with so much certainty as was 

 desirable. 



CidariS Thonarsii Valenciennes. 



Cidaris Thouarsii Agassiz and Desor, Catal. Rais. des Echinides, Ann. des Sci. Nat., 

 vi, p. 326, 1846. 



Mr. Bi'adley has sent numerous specimens of this species from 

 Panama and the Pearl Islands, where it occurs among rocks and in 

 cavities at low-water. It has been described from the Galapago 

 Islands and California (Ag. and Des. Cat. Rais.). The Smithsonian 

 Institution has presented specimens from Cape St. Lucas, collected by 

 J. Xantus.* 



This is closely allied to C. annulata Gray, common at Aspinwall 

 and the West Indies, but differs in the wider and more closely granu- 

 lated median area of the interambulacra and in having much stouter 

 and relatively shorter spines, which are more coarsely sculptured on 

 the surface. The large spines are round, largest a short distance 

 above the base, and then slightly and gradually diminish to near the 

 ends, which are enlarged and obtuse. A specimen V26 inches in 

 diameter has the large spines 1-3 long, -15 in diameter. The small 

 spines at their bases ai'e flat, thin, spatulate, obtuse at the ends. The 

 ovarian plates form a regular five-rayed star, more distinct than in C. 

 annulata. Color of the larger specimens, when dry, deep brown, 

 with the larger spines light purplish brown. Young specimens, in 

 alcohol, have the spines light purple, banded with white. 



Diadema Mexicana A. Agassiz, Bulletin Mus. Comp. ZooL, No. 2, p. 20, 1863. 



We have received from the Museum of Comparative Zoology, 

 through the kindness of Mr. A. Agassiz, a good example of this spe- 

 cies, collected by him at Acapulco. In the Smithsonian Institution 

 there are a few young specimens, apparently of the same species, 

 collected at Cape St. Lucas by J. Xantus. 



Our specimen has a test 2*25 inches in diameter, 1*25 high; diame- 



* Sent in abundance from La Paz, by J. Pedersen, — Reprint 



