BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 13. AFU. IV. N:0 5. 1(>7 



Avcre determmed by Agassiz as E. grandinosa, and given under 

 that name by Desmoulins in 1869, witli Pervi for their habitat, 

 as stated by the vender. Troschel bas Chile, and de Loriol 

 writes me that the specimcn be formerly bad lent Troschel 

 and obligingly placed in my hands, bad been acquired at Paris 

 from a person wbo was sure of its having been brought from 

 Peru. Add to all this, last bvit not least, that the 27th plate 

 in the Voyage of Lapeyrouse, redeemed from oblivion by 

 Troschel, is inscribed: >Echinoids from the X. W. coast of 

 America>, and contains figiires, 4 — 9, obviously representing 

 the Arbacia orrandinosa Val., and it becomes certain that the 

 original of Valenciennes really eame from the Pacific coast 

 of America, and that the other habitat given in the »Catalogiie 

 Raisonné^: Carthagena, the sea-port of New-Granada, on the 

 Caribbean side, is a mistake probably caiised by the confoun- 

 ding in the Paris Museum of the species with that called au- 

 stralis bv Troschel and pustulosa by some authors, which 

 lives on the coast of Brazil and presumably also nearer the 

 Isthmus on its eastern side. It beino- so, the A. grandinosa 

 Val. is to be regarded as a representative, on the Pacific side, 

 of the Atlantic type of Arbacia bearing spines all över, just 

 as the Echinometra Van Brunti Al. Ag., and another form, 

 are representatives on the Pacific side of the E. Lucunter L. 

 of the Atlantic, and the Meoma grandis of the M. ventricosa, 

 not to mention numerous other instances of representative 

 Mollusks, Crustaceans and other animals, now well known to 

 appear on both sides in nearly related forms. 



The Pacific Ocean type of Arbacia is exhibited by the 

 species presenting a dorsal »står», that is in which the five 

 disks of the interradia are without spines and more highlv 

 coloured. Four of them live on the western coast of America, 

 while one alone is Atlantic. The A. Dufresnei, first described 

 by Blainville, and the A. alteriians Troscilel, in both of 

 which the uneqiial development of the tubercles is ver}^ con- 

 spicuous, are the southern species, inhabitants af the Straits 

 of Magellan and the coast of Chile. They are succeeded on 

 the coasts of Peru and the Isthmus by the A. spathuligera 

 Val. and at Payta, Panama, California by the A. stellata. 



The close affinity between the Arbacia stellata Blv. and 

 A. puuctiilata Lamck. bas been more than ouce remarked 

 upon. The former comes nearer to the latter than to the 



