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 Eev. A. Nicol. 



Genus III. IDMO^N'EA, Lamouroux. 



Gen. Char. Polypidom calcareous, divided dichotomously, 

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

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



1. Idmonea Atlantica, E. Forbes. 



Hab. Zetland Seas, Prof. E. Eorbes; 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. Pour-tenths of an inch 

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

 fessor E. Porbes, who has another species from the ^gean 

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

 lection of Mr. Stokes there is one from Kamtchatka. 



