CARIBEAN AND PANAMIC ECHINI. 235 



An analysis of the representative species at different depths on both sides 

 of the Isthmus of Panama shows a surprising similarity. Since the publi- 

 cation of the '• Blake " lists, 1 the number of representative species has 

 been markedly increased by the discoveries of the " Albatross " in 1891. 

 The littoral species with a range of something beyond 100 fathoms, and 

 some of the species having an abnormal range extend into the Continen- 

 tal slope or even beyond to the abyssal region ; these number no less than 

 thirty-four species on the Caribean side. With the exception of Cidaris 

 they belong to tertiary genera of comparatively recent periods. On the 

 Panama side they are represented by twenty-seven species. Of these, two 

 are genera (Lovenia and Astropyga) not represented on the West Indian 

 side ; while of the thirty-four West Indian species Echinus, Echinocyamus, 

 Pygastrides, Echinoneus, Echinolampas, and Echinocardium are not found on 

 the Pacific side. The other genera are represented on both sides by closely 

 allied species, which may be regarded as strictly representative species. 



Many of the West Indian littoral genera have a wide geographical dis- 

 tribution both in the Atlantic and Pacific. Some of the genera are strictly 

 American, or on the Pacific side of the Isthmus there are some American 

 and a few Indo-Pacific genera. They are : Cidaris, Dorocidaris, Diadema, 

 Echinometra, Echinus, Strongylocentrotus, Echinocardium, Brissopsis, Bris- 

 sus and Schizaster. 



The following: genera are West Indian and Atlantic and have not been 

 found on the Panama side, but occur in the East Indian Archipelago and 

 Western Pacific : Echinus, Echinocyamus, Echinoneus, Echinolampas. 



The following are West Indian, Panamic, and Indo-Pacific : Toxopneustes, 

 Hipponoe, Echinanthus, Metalia, Periaster. 



The following genera occur on both sides of the Isthmus, and are emi- 

 nently American : Mellita, Encope, Agassizia, Moira. Arbacia is American 

 and Atlantic ; Astropyga is Panamic and Indo-Pacific. 



When we come to the continental slope, the dredgings of the " Blake " 

 were far more numerous in that region than those of the " Albatross," 

 no less than 316 Stations having been occupied by the " Blake " in the 

 continental area of the West Indies, which is also one of the richest regions 

 of its kind, not only for Echini but also for all classes of invertebrates. 



On the West Indian side there are thirty-three species of Echini repre- 

 senting twenty-four genera. On the Panamic side we have only nine 



i "Blake" Echini, p. 84. 



