158 MEMBRANIPORIDJE. 



ever, is taken from a specimen without ovicells ; and in 

 such cases the avicularium is almost universally so placed. 

 Alder's, on the contrary, represents a fertile group ; and 

 whenever the oviccll is present, the direction of the avicu- 

 larium is always reversed and it points upwards. This 

 remark applies equally to other species. 



MEMBRANIPORA SOLIDULA, Alder and Hincks. 



Plate XX. figs. 7, 8. 



MEMBRANIPORA SOLIDULA, Hincks, Proc. Dublin Univ. Zool. & Botan. Assoc. 

 ii. pt. 1 (1860), 75. 



Zooecia oval, with a crcnulate margin, the membranous 

 covering opaque and of a dull waxy appearance, lying 

 very much on a level with the margin, so that the 

 zoarium presents a very flat surface ; four spines at the 

 upper end of the cell immediately above the semicircu- 

 lar orifice j frequently one or two prominent smooth 

 nodules below the base of the cell. Ooecia globose, 

 subimmersed, shallow, smooth, with a strong thickened 

 ridge across the upper part. Avicularia none. 



RANGE OF VARIATION. Slight differences in the shape 

 of the cells, which are occasionally somewhat narrowed 

 towards the top and expand below. 



HABITAT. On shells, stones, &c., from moderate depths 

 to deep water. 



LOCALITIES. Off the coast of Antrim (Hyndman) : 

 Guernsey (T. H.) : Hastings (Miss Jelly). 



Some of the peculiarities of tlys species were pointed 

 out to me by the late Mr. Alder ; and I have therefore 

 associated his name with it as well as my own. 



The cells are small and regular in form, with a prettily 



