DIOSTOPORA. 277 



the mouths are raised, with a round oblique plain aperture. 

 The finest and largest specimens I have seen were on the 

 valves of Pecten ingens, from the islands of Tiree and Coll, 

 sent to me by my friend, the Rev. A. Nicol. 



Genus III. IDMONEA, Lamouroux. 



Gen. Char. Polypidom calcareous, divided dichotomously, 

 erect, celluliferous on one side only ; cells tubular, in transverse 

 rows, divided into two sets by a medial longitudinal line. 



1. IDMONEA ATLANTICA, E. Forbes. 



Hab. Zetland Seas, Prof. E. Forbes; island of Coll, 

 D. L., from the Eev. Mr. Nicol. 



Erect, white, firm, dichotomous; branches spreading la- 

 terally; the cells tubular, forming a series of transverse 

 rows on each side of the coral; the rows are on one side 

 alternating with those of the other. Four-tenths of an inch 

 in height. This is one of the numerous discoveries of Pro- 

 fessor E. Forbes, who has another species from the ^Egean 

 Sea, somewhat similar to the 7. Atlantica ; and in the col- 

 lection of Mr. Stokes there is one from Kamtchatka. 



