MEMBRANIPORA DUMERILII. 157 



Flustra foliacea (Alder) : Arran ; Dogger Bank ; Isle of 

 Man ; South Devon, abundant on shells, &c. ; Ilfracombe, 

 on Laminaria ; Cornwall, off the Deadman, in 60 fathoms, 

 on stone (T. H.) : Hastings (Miss Jelly) : Antrim (Hynd- 

 man) : &c. 



Geographical Distribution. Scandinavian Seas 

 (Smitt) : ? Mediterranean (Savigny) : France, south-west 

 (Fischer). 



Range in Time. Coralline Crag, on shell (S. Wood). 



This species is distinguished from the last by several 

 well-marked characters, though the two forms are nearly 

 related. The cells are much smaller than those of M. 

 unicornis, and not so regularly oval. There is, indeed, 

 some amount of variation in form ; but the cell in M. 

 Dumerilii is usually narroAved towards the top and ex- 

 pands below ; while that of the kindred species is of a 

 pretty uniform elongate-oval shape. The chief difference 

 lies in the ovicell, which is globose, or (very often) consi- 

 derably elongated, and strongly granulated ; that of M. 

 unicornis, on the other hand, is smooth, with a rib across 

 the front of it, just above the margin, and a prominent 

 avicularium on the summit, " giving the whole," as Alder 

 has remarked, " the appearance of a Phrygian bonnet." 

 The general aspect of the two species is very different. The 

 lacework of M. unicornis is much coarser than that of its 

 ally, and wants its remarkably delicate and pearly texture. 



The enormous development of one of the spines in 

 front of the ovicell, which is so common in the present 

 species, I have never noticed in M. unicornis. 



Smitt remarks that the form which he refers to M. Du- 

 merilii differs from that which Alder figures [I.e. pi. viii. 

 fig. 5) in having the mandible of the avicularium di- 

 rected towards the centre of the colony. His figure, how- 



