MUSEUM OF COMPARATIVE ZOOLOGY. 299 



Everything either remains at a short distance below the surface, or is 

 blown out to seaward of the islands. The phosphorescence, in conse- 

 quence, is far less brilliant than in the Gulf of Mexico, although occa- 

 sionally the masses of Cteuophorro (a species of Mnemiopsis), swimming 

 at diflFerent depths, produced a very striking illumination : sudden 

 flashes of light suddenly appearing as if coming from great balls of fire 

 floating a short distance below the surface. The most striking phospho- 

 rescent phenomena were produced by a small Annelid, allied to Syllis, 

 which moved over the surface of the water with great rapidity, per 

 forming the most remarkable gyrations, and tracing its path, which 

 remained phosphorescent for a short time, by a brilliant line of light. 

 Among the deep-water forms, several of the species of Gorgoniaj and 

 Anthipates (especially Riisea) showed a bright bluish phosphorescence 

 when coming up in the trawl. One Ophiuran also, like one of the Med- 

 iterranean species mentioned by Panceri, was exceedingly phospho- 

 rescent, emitting along the whole length of its arms at the joints a 

 brilliant, bluish-green light. 



One of the most interesting results reached by this year's cruise is 

 the light thrown upon the former extension of the South American 

 Continent, by the soundings taken while dredging, and those subse- 

 quently made in the passages between the islands by Commander Bart- 

 lett. These, together with the soundings already known, enable us to 

 trace the outline of the old continent with tolerable accuracj', and thus 

 obtain some intelligible, and at the same time trustworthy, explanation 

 of the peculiar geographical distribution of the fauna and flora of the 

 West India Islands. As is well known, Cuba, the Bahamas, Hayti, 

 and Porto Rico, instead of showing, as we might naturally assume from 

 their present proximity to Florida, a decided aflBnity in their fauna and 

 flora with that of the Southern United States, show, on the contrary, 

 unmistakable association with that of Mexico, Honduras, and Central 

 America; the Caribbean Islands show in part the same relationship, 

 tliougli the affinity to the Venezuelan and BraziUan fauna and flora is 

 much more marked. 



In attempting to reconstruct, from the soundings,* the state of things 

 existing in a former period, we arc at once struck by the fiact that the 

 Virgin Islands are the outcropping of an extensive bank. The greatest 

 depth between these islands is less than 40 fathoms, this same depth 

 being found on the bank to the east of Porto Rico, the 100-fathom line 



* See the maps accompanying this letter, for which I am indebted to the Hon. 

 Carlile P. Patterson, Supt. U. S. Coast Survey. 



