BARBADOS-ANTIGUA REPORTS 39 



represents the extreme outer limits of a tropical and subtropical 

 faunal region the center of which is the Indo-^Ialayan region. 



The types inhabiting it, that is to say occurring only on the 

 extreme periphery of the Indo-Pacific faunal area (of which the 

 Mediterranean Sea was at one time a part) may be considered, 

 therefore, as relics of a previous fauna at one time characteristic 

 of the central Indo-Malayan region from which they have now 

 been extirpated through the competition of younger and more 

 efficient types. 



The same facts are brought out equally well in many other 

 groups of marine animals, and are also reflected in a modified 

 way in the terrestrial faunas. 



In the faunas of the colder seas all intergradations are found 

 between types which are quite unique, and types differing little 

 or not at all from others in the Indo-Malayan region, and this 

 intergradation is complete enough so that we are justified in 

 considering the fauna of the colder waters as similarly ultimately 

 derived from the (past or present) fauna of the East Indian 

 region largely through the intermediary of deep water forms. 

 Some of these genera of the colder waters, as Astriclypeus and 

 GLYPTOcroARis, are extraordinarily restricted in their distribu- 

 tion and rare, while others are abundant and widely spread. 



One of the peculiarities of the West Indian ophiuran fauna is 

 the relatively poor representation of Ophiotrichidae. This family 

 includes 13 genera and 157 species of which 126 belong to the 

 genus Ophiothrex, occurring in all the warmer portions of the 

 recent seas and represented by 7 species in the West Indies. One 

 monotypic genus, Ophiotrichoides, is only known from the Cape 

 Verde Islands, but the remaining 11 genera are exclusively 

 Indo-Malayan. All of the species of this family are more or less 

 conmmensal in habit, and some are almost parasitic. The species 

 of four of the genera, Ophiomaza, Ophio.ethiops, Ophiophthi- 

 rius and Ophiosph.era, live upon comatulids. In one genus, 

 Ophiopterox, the arm spines are webbed together and resemble 

 little fins which has given rise to the idea that it is able to swim. 



The greatest mystery connected with the Caribbean ophiurans 

 concerns the genus Ophioblexna. The only known species, 

 Ophiohlenim antillensis, was described in 1859 from two speci- 

 mens collected at Water Island, St. Thomas. In spite of all the 



