CLARK: THE CIDAKIDAE. 185 



southern coast of Asia with the adjoining islands, through the East Indian archi- 

 pelego and out into the Pacific, as far as the Solomon, Fiji, and Hawaiian Islands. 

 Curiously enough, metularia does not seem to reach either Japan (except the Liu- 

 kiu Islands) or Australia. The only difference that can be detected between 

 Mauritian and Hawaiian specimens is that, in the latter, the median ambulac- 

 ral area is somewhat broader and flatter, but the difference is very slight and 

 inconstant. 



Cidaris tribuloides. 



Cidarites tribuloides Lamarck, 1816, Anim. s. Vert., 3, p. 56. 

 Cidaris tribuloides Agassiz, 1835, Prodrome, p. 188. 



Plate Id, Plate 3, flgs. 1-3, Rev. Ech., A. Agassiz, 1872. 



Little need be said further in regard to this well-known species, save that the 

 primary spines are frequently cross-banded, especially in young specimens, and in 

 old specimens are almost always more or less encrusted with colonies of Bryozoa, 

 and similar foreign material. The relative length and thickness of the primaries 

 differ to a remarkable degree in specimens from different localities. The general 

 appearance of specimens from the Cape Verde Islands is thus strikingly different 

 from that of the ordinary West Indian form. On the other hand, many of the 

 specimens dredged in the West Indies, by the " Blake," have the primaries so long 

 and slender that there is a noticeable superficial resemblance to Tretocidaris affinis. 

 Connecting forms between the extremes are, however, common. The stalks of the 

 large globiferous pedicellariae have no " limb." The geographical range is con- 

 fined to the Atlantic Ocean, from the Bermudas and Azores on the north to Brazil, 

 the Cape Verde Islands, and Cape Palmas on the south. In the Museum are 

 several old tests without spines, which are almost certainly this species, labelled 

 " Mer Rouge," but a mistake in labels is always possible, and these have doubtless 

 been mixed at some time with West Indian specimens. There is also a very small 

 (5 mm. h. d.) but perfect specimen from "51° 26' S. and 68° 5' W., 57fths.," 

 collected by the " Hassler." If there has been no mistake, this would indicate a 

 remarkable southern range. Small specimens from Ascension Island, Atlantic 

 Ocean, in the collection of the National Museum, like those collected by the 

 "Challenger" at Bahia, and Fernando Noronha, Brazil, have verticillate swellings 

 on the primaries, but are not otherwise peculiar. 



Cidaris thouarsii. 



Cidaris thouarsii Agassiz and Desor, 1846, Cat. Rais. Ann. Sci. Nat. (3) 6, p. 326. 



Plate 10, Jap. Seeigel, Doderlein, 1887. 



This is the well-known substitute for tribuloides on the west coast of America. 

 It is easily distinguished from that species by the color and other characters men- 

 tioned above. Its range is comparatively limited, however, as it is not known from 

 south of the equator (save in the Galapagos) nor from north of the Gulf of Cali- 



