MEMBRANIPORA CRATICULA. 147 



Membranipora CRATICULA, Aider. 



Plate XIX. fig. 7. 



Flustra lineata, Couch, Corn. Faun. pt. iii. 124, pi. xxii. fig. 15 ? 

 Membranipora craticula, Alder, North. Cat., Trans. Tyneside Field Club, 



iii. 144, pi. viii. fig. 3. 

 Membranipora lineata, 1, forma craticula, Sniitt, (Efvers. K. Vet.-Ak, 



F5rh. 1867, 363. 



Zocecia small, in very regular, radiating, linear series, oval, 

 somewhat narrowed above ; the margin with about 

 thirteen spines, of which the two uppermost pairs are 

 erect and often of very great length; the rest flattish, 

 glistening, closely set, bent inwards, and meeting across 

 the cell, especially crowded together at the bottom of it : 

 an avicularium, with acute mandible directed downwards, 

 at the base of the cells. Ooecia rather small, smooth, 

 cylindrico-globose, with a rib across the middle; an 

 avicularium at the top or at one side, with the mandible 

 pointing upwards. 



Primary cell subcircular; aperture terminal, with about 

 nine marginal spines. 



Colonies forming small flabellate or subcircular patches, 

 with a soft spongy look, from the great number of 

 closely-set spines. 



Range of Variation. I have observed very little variation 

 in this species. There are slight differences in the number 

 of the spines ; but the chief features are very constant and 

 uniform. 



Habitat. On shells, &c., from shallow to deep water, 

 and on littoral sea-weeds. 



Localities. Northumberland and Durham, on Modiolce 

 from deep water (Alder) : Isle of Man, very abundant on 

 shells dredged off Maughold Head; Oban (T. H.) : St. 

 Andrews, occasionally in deep water (Dr. M'Intosh) : 



