Verrm.] 324 



genus, SfepTianocora, attaining no great size. The Millepora alcicornis 

 L., so abundant on the Atlantic side, even at Aspinwall, is not repre- 

 sented at Panama, or on the Pacific coast, by any species belonging to 

 the same family, but Pocillopora, an almost exclusively Pacific and 

 Indian Ocean genus, is the most nearly allied form found at Panama ; 

 if indeed, the latter proves to be an Acalephian coral, as Prof. Agassiz 

 supposes. 



Consequently at Panama, and on the entire western coast of Cen- 

 tral America within the tropics, no true coral reefs occur. The few 

 small species of calcareous corals merely encrust the rocky reefs in 

 some places, and cluster in their crevices and pools, and whenever calca- 

 reous deposits occur about the reefs, they are com^xjsed chiefly of broken 

 shells with mud and sand. The Gorgonidce, also, are entirely different 

 on the two sides. The most prominent West Indian genera, Pterogor- 

 gia, Xiphigorgia, Plexaura^ Plexaurella and Eunicea, each represented 

 by several species at Aspinwall, Florida, etc., do not, so far as yet 

 known, occur at all on the Pacific coast of Central America.* The 

 Gorgonia Jlabellwn of the West Indies, is represented by three allied 

 species at Panama, but of small size. The typical Gorgonice are 

 about equally represented on each coast, but the forms are very dis- 

 tinct. The genus Muricea is most fully represented at Panama, no 

 less than six species occuring there, while in the West Indies there 

 are but four well established species. The forms of this genus occur- 

 ing at Panama, are mostly thickly branched and rigid ; while those of 

 the West Indies usually have long, slender, and more flexible branches. 



Of true corals the genus Astrangia is peculiarly characteristic 

 of the Panama region, from whence we have five species, besides 

 two others belonging to closely allied genera. In the West Indies two 

 species occur, A. solitaria Verrill (7 A. neglecta Dueh.) and A. gran- 

 ulata Duch. On the coast of South Carolina and Georgia, A. astrcei- 

 formis E. & H., and on the coast of Long Island Sound A. Dance 

 Ag., represent this genus. Another species allied to A. Edivardsii] 

 Verrill, and perhaps identical, occurs at Terra del Fuego. The re- 

 maining described species, A. Michelini E. & H., is of unknown ori- 

 gin. The single previously described species of Ulangia ( U. Stokes- 

 iana E. & H.) is from the Philippines; and the only other known 

 Phgllangicij which is living (P. Americana E. & H.) inhabits the West 

 Indies. 



These remarkable diflferences between the two faunse do not favor 

 the theory that has been entertained by some geologists, that there has 

 been a communication between the two oceans at this point, and that 



* A species of Plexaiira (P.facosa) occurs, however, on the coast of California 

 near San J>ancisco. 



t This name I propose for the species called Astrangia Dance by Edwards and 

 Haime, not A. Dance Agassiz, of previous date. 



