226 LITTORAL DISTRICTS. 



LusiTAsriAN District (PL B). 



Leaving the North Atlantic District, we come to the strictly Mediterra- 

 nean species, consisting of Centrostephahus longispinus, Echinus microtuber- 

 culatus, Sphaerechinus granulans, Echinus nielo, Echinocardium mediterra- 

 neuin, and Schizaster canaliferus, overlapping to the north, as far as the 

 Portuguese Coast, and even, for some species, as far as the English Channel, 

 the North Atlantic European fauna, stretching westward as far as the Azores, 

 and to the south as the Cape Verde Islands. Many of the species of the Lu- 

 sitanian District occur at the Cape Verde Islands with strictly tropical Afri- 

 can species, and a lew of the West Indian species, extending to the Atlantic 

 Coast of West Africa, and combining with the North Atlantic species found 

 at the Azores, in the Mediterranean, and the Atlantic Coast of West Africa, 

 give to the Lusitanian District, north and south of the Straits of Gibraltar, 

 an extreme])- mixed character. 



The West Indian species are Cidaris trilmloides | Diadema setosum cosmo- 

 politan!. Echinometra subangularis. Chpeaster suhdepressus. Strongylocen- 

 trotus lividus and Axbacia pustulosa belong also to the Mediterranean 

 species, but extend farther north and south than the purely Mediterranean 

 species, and also reach across to Brazil. 



The North Atlantic and West European species which extend into this 

 district have already been enumerated. 



West African District (PI A). 



Of the Tropical Atlantic African District we know as yet too little to say 

 anything very definite of its range. The existence of two species of Rotula 

 and an Echinolainpas, combined with Mediterranean species, as well as West 

 Indian species to the North, is all we know, while the southern limit of this 

 district is as yet entirely undefined, and the coast between the equator ami 

 the Cape of Cood Hope is completely terra incogniln. The only thing we 

 know of that district is the presence of Echinometra subangularis at St. 

 Helena and Ascension, hut these islands are not sufficiently close to the 

 mainland to give us any clew to the character of the Echini found there. 



South Circumpolar District (PL B\ 



The southern extremity of Africa is characterized by a very small number 

 ol' species, the northwestern limit of which is entirely unknown, while the 



