MEMBRANIPORA TRIFOLIUM. 167 



shell; Guernsey (T. H.) : Antrim (Hyndman) : Peter- 

 head and Wick (C. W. P.) . 



Geographical Distribution. Algiers (J. Y. J.) : Bay 

 of Gibraltar (M'Andrew and Landsborough) : Adriatic, on 

 Tellina depressa (Heller). 



Membranipora trifoliuMj S. Wood. 



Plate XXII. figs. 5, 6. 



Flustra trifolivm, Searlcs Wood, Ann. IS^. H. ser. 1, xiii. 20. 

 Membranipora tripolium, Busk, Crag Pol. 32, pi. iii. figs. 1, 2, 3, and 9 



(part). 

 Membranipora .solida, Packard, Labrador Anim. (1860), 8, fig. 2. 

 Membranipora sacculata, Norman, Ann. N. H. ser. 3, xiii. (1864), 88 



(8 Sep.), pi. xi. fig. 3. 

 Membranipora Flemingii, forma trifolium, Smitt, CEfv. K. Veten.sk.- 



Akad. Forh. 1867, no. 5 ; Krit. Forteckn. pt. iii. 367 and 



405, pi. XX. fig. 42. 



Zocecia lozenge-shaped, or ovate, or elongate, arched and 

 wide above and narrowed downwards ; the lower part 

 of the area covered in by a thin, minutely granular 

 lamina 5 aperture ample, trifoliate; margin elevated, 

 crenated. Avicularia sparingly developed, raised, 

 placed between the cells ; mandible acute, directed up- 

 wards or downwards. Ocecia semielliptical, smooth, 

 but having on the front a triangular space, bordered 

 by a raised line, which is minutely granular. 



Colonies of a pale olivaceous -green colour. 



Var. a {quadrata) . Margin of the cells very prominent 

 and strongly crenated, rarely two spines at the top, one 

 on each side. Occasionally a prominent avicularium 

 on the lamina, near the bottom of the cell, placed 

 obliquely ; mandible pointing dowmvards and outwards. 

 Ooecia globose, bordered in front by a raised line, 

 inclosing a somewhat quadrangular space, which is 

 minutely granulated. 



Colonies forming subcircular, reddish-brown crusts. 



