ALCYONARIAN CORALS 125 



nominis causa, quod in duritiam lapidis mutatur emollitum 

 in mari ; banc fascinationibus resistere adiirmant." 



Such a definition of a coral which asserts that it is soft 

 in the water and turns hard on exposure to the air, and that 

 it has the power of resisting fascinations, may not be satis- 

 factory to the modern zoologist, but it, at least, lends support 

 to the view that the Romans regarded the Gorgonians as 

 something of the same nature as corals. 



At the present day the generic name Gorgonia is very 

 much more restricted than it was even at the beginning of 

 the last century, and a host of new generic names have been 

 invented for many of the Gorgonians of the old writers. 

 These genera are divided into six families, of which four — 

 the Gorgoniidae, Gorgonellidae, Plexauridae, and Prim- 

 noidae — are usually represented in museums by typical 

 specimens. 



There are three principal characters distinguishing the 

 Gorgoniidae from the other five families. The axis is horny 

 without any admixture of calcareous matter, the coenen- 

 chym is thin, and the polyps are retractile. 



The axis is variously but usually profusely and delicately 

 ramified, and in dried and retracted specimens the position 

 of the zooids is represented by more or less prominent 

 mounds or verrucae on the coenenchym. 



Gorgonia. — One of the most familiar of the Gorgoniidae 

 is the Gorgonia flahellmn'^ of the shallow waters of the 

 West Indies and other localities of the tropical Atlantic, 

 which forms delicate fan-shaped structures by the profuse 

 anastomosing of slender branches arranged in one plane. 



Other genera of Gorgoniidae, such as Leptogorgia and 

 Pterogorgia, form immense tufts or shrubs ending in long 

 delicate branches which bend in all directions with the 

 movements of the water, like grass in the wind, and with 

 their brilliant purple, yellow, and red colours contribute to 

 the brilliancy of the pools of the coral reefs in which they 

 are often found. These beautiful and variously coloured 

 corals form an effective display in a museum case. 



In some respects, however, the most interesting member 



^ Rhipidogorgia. 



