]s[o. 6. — Reports on the Results of Dredging, under the Supervision 

 of Alexander Agassiz, in the Caribbean Sea in 1878-79, and 

 along the Atlantic Coast of the United States during the Summer 

 0/I88O, by the U. S. Coast Survey Steamer "Blake,'' Commander 

 J. E. Bartlett, U, S. N., Commanding* 



(Published by permission of Carlile P. Patterson and J. E. Hilgaed, Superin- 

 tendents of the U. S. Coast and Geodetic Survey.) 



XX. 



Report on the Ophiuroidea. By Theodore Lyman. 



The West Indies are the hotbed of Echinodermata. Out of less than 

 six hundred living species of Ophiuroidea now known, about one hun- 

 dred and fifty-five, or more than a quarter, are from that region ; and 

 for the round Echinoderms the proportion is even larger. Beginning at 

 low-water mark, this fauna descends to 1,568 fathoms ; and, having its 

 centre in the Caribbean Sea and the Gulf of Mexico, it sends branches 

 northward at least as far as South Carolina, and southward to Brazil. 

 In the present state of knowledge, it seems a well-marked fauna, con- 

 taining a great number of distinctive forms, although there occasionally 

 occur species from other marine regions, such as Ophioscolex glacialis and 

 Astronyx Loveni. This appearance of limitation may come in part from 

 the special investigations in this area ; for it is to be borne in mind 

 that the U. S. ships " Corwin," " Bibb," " Hassler," and " Blake " have 

 dredged in about 570 stations, chiefly along the line of the Antilles, 

 and from the Dry Tortugas to Cape Florida. In addition to these, 

 some hauls were made by Dr. William Stimpson, and by the naturalists 

 of the " Challenger." 



Nearly all known genera of Ophiuroidea are there found, the most 

 notable exceptions being Ophioplocus, Ophioplinthus, Ophiopholis, 

 Ophiarachna, Ophiarthrum, Ophiomastix, and Trichaster. 



Among Ophiurans, as in other animals, we find that certain genera 



* In this paper are included six new species from the dredgings of the " Porcu- 

 pine " and the " Ciiallenger," which are published by permission of the Lords 

 Commissioners of tlie Treasury. 



VOL. X. — NO. 6. 



