36 THE VOYAGE OF H.M.S. CHALLENGER. 



tions. Actinometra pulchella occurs at every one of these eleven stations, excepting 

 No. 174 in the South Pacific; while it is the only Actinometra represented at six at 

 least of them, including three of the deepest ones. This may be partly explained by the 

 fact that only one of these stations was in the Pacific, all the remainder being in the 

 Atlantic and the Caribbean Sea, but it is especially noteworthy because Actinometra 

 jmlchella is a dimorphic species, some forms having only ten arms, and some having 

 bidistichate series on one or more rays. The three species obtained by the Challenger at 

 Station 174 were all multibrachiate forms expressing widely different types of the genus ; 

 but the "Blake" dredged a ten-armed species at 450 fathoms, off Havana, and the two 

 deepest stations in the Caribbean Sea where Actinometra pulchella occurred also yielded 

 ten-armed species. 



These ten-armed forms of Actinometra which occur in the Caribbean Sea and along 

 the South American coast, represent an entirely different type of the genus from the ten- 

 armed species of the eastern hemisphere. The latter mostly belong to the type of Actino- 

 metra Solaris, with syzygies between the two outer radials, though a few forms occur in 

 which these joints are united by bifascial articulation, as in nearly every Antedon and 

 in the Actinometra meridionalis of the Caribbean Sea (PI. LVI. fig. 1). The Solaris- 

 type, however, has not yet been discovered in the Atlantic. 



Of the multibrachiate species of Actinometra the tridistichate type seems to be the 

 more extensively distributed and not the bidistichate one as in the case of Antedon. Thus, 

 for example, Actinometra parvicirra (o.3.(3).(3)) occurs in South Africa, Timor, Ceram, 

 the Philippines, Japan, the Friendly Islands, and even on the coast of Peru, so that it 

 has a range in longitude of some 260°, occurring everywhere but in the Atlantic. This 

 is only approached by the ten-armed Antedon carinata, which occurs on both coasts 

 of South America and across the Indian Ocean from Java to Zanzibar. 



