NATURAL SCIENCES 0? PHILADELPHIA. 355 



When specimens have remained some time in alcohol the spines become 

 ash colored. 



Colobocenlrotus can readily be distinguished from Podophora by its peculiar 

 ambulacra, the tubercles of which are arranged in four vertical rows, the 

 median space raised above the poriferous zone ; there is a strong depression 

 between the tubercles of consecutive plates. The interambulacral plates are 

 separated by a well marked suture on the abactinal side. 



Parasalenia gratiosa A. Ag., Bull. Mus. Comp. Zool., 1863. 



" Body everywhere black ; spines dark olive, with a ring of white at base 

 of each. 



"Among madrepores in 1 f. Port Lloyd, Bonin Islands." (W. Stimpson.) 



ECHINOMETRA BRUNEA A. Ag. 



Differs from E. lucunter by the great height of the polar diameter of the test, 

 as well as the uniform size of the tubercles and spines. 

 " Among coral at 1. w. m., Bonin Islands." (W. Stimpson.) 



ECHINOMETRA LUCUNTER Lamk. 



"Hilo, Hawaii." 



" On the coral reefs of Tahiti." 



" Body always dark purple; spine greenish ; mouth red. Bonin Islands, in 

 crevices of rocks and coral in 4th 1." (W. Stimpson.) 



"Loo Choo Islands. 



" Ousima." (W. Stimpson.) 



These specimens have been examined side by side with specimens compared 

 to the originals of Lamarck sent to the Museum at Cambridge, through 

 the kindness of Prof. Valenciennes. This species has been so often quoted by 

 different explorers as occuring at localities as far apart as the West Indies, 

 the Cape of Good Hope, Mauritius, East India Islands, in the Pacific Ocean, at 

 the Low Isl., the Sandwich Isl., &c, that it became an interesting question 

 carefully to compare specimens from these different localities. It became at 

 once apparent that we had one species in the West India Islands, (E. Michelini 

 Des.,) one species at Mauritius, Zanzibar, (E. acufera,) associated with E. 

 lucunter Lamk., so that the true E. lucunter of Lamarck is not confined to the 

 Pacific Ocean, and seems to enjoy a very extensive range of distribution, 

 Besides the localities here mentioned there are specimens in the Museum of 

 Comparative Zoology at Cambridge from the Kingsmill Islands, the Society 

 Islands and the Navigators Islands, and also from Tor in the Red Sea, which 

 have been received from the Imperial Museum at Vienna. 



Heterocentrotus mammillatus Br., appears almost always associated with E. 

 lucunter. These two Echinoids are particularly characteristic of the great Belt 

 which extends on both sides of the Equator from the east coast of Africa to the 

 Sandwich Isls. Eipponoe' sardica Gray, which is also quoted as occurring with 

 these two species, may prove identical with Hipponoe violacea A. Ag., but the 

 materials on hand at present are not sufficient to decide this point, as it is ex- 

 tremely difficult to ascertain what are specific differences in this family of Hip- 

 ponoidae, owing to the great difference between the young and the adult. 

 Young specimens of the common Tripneustes ventricosum, from Florida, having 

 even been placed into a new genus, Helieckinus, by Girard, (Helieckinus Gouldii, 

 Gir.) Supposing, formerly, that this species (E. lucunter) had not been described, 

 and many specimens having found their way into other Museums from the 

 collection at Cambridge under the name of Echinometra picta A. Ag., I take this 

 opportunity to correct my mistake. 



Arbacia aequituberoulata Gray, Proc. Zool. Soc, 1855. 

 " Madeira." 

 " Porto Praya, Cape de Verde Islands." (W. Stimpson.) 



1863.] 



