134 CLASS II.— ORDER II. 



nearly equal. The substance of the part connect- 

 ing the articulations in these Polypidoms possesses 

 a rigidity and fragility, somewhat resembling the Isis 

 when divested of its polypiferous rind. 



The Amphiroas multiply by tubercular ovaria, 

 placed on the cretaceous part of the articulations y 

 these ovaria are sometimes abundant, and sometimes 

 scanty ; they appear organised like the pyriform ovaria 

 of the Corallinas and Janias. 



The Amphiroas differ in their forms more than the 

 Corallinas ; in the latter the articulations are nearly 

 alike : but in the former they are sometimes found 

 cylindrical in the stem, compressed in the branches,, 

 and either flat or spoon-shaped at the extremities. 

 They vary equally in their ramifications ; dispersed 

 in some, dichotomous in a few, and in others ver- 

 ticillated once or many times, the verticils in many 

 species consisting of numerous branches; some- 

 times all these characters are found united in the 

 same individual. 



Their colours are similar to those of the Corallinas. 



They do not exceed a decimetre in height, nor are 

 they ever less than three or four centimetres. 



They are usually found in warm and temperate 

 latitudes. I am inclined to think they are not inha- 

 bitants of the colder regions. They are attached to 

 rocks and other hard substances, never parasites on 

 marine plants. 



The Corallina Officinalis, or Corsican moss, is some- 

 times chiefly composed of polypidoms of this genus. 



