161 MEMBRANIPORID/E. 



are usually a very conspicuous feature. Of the four at 

 the top, which are found in young marginal cells, one or 

 two seem to be deciduous and soon disappear. Six usually 

 remain, of which the two uppermost are tall and slight 

 and sharply pointed, and the rest tubular and compara- 

 tively stout. One of them is separated from its companions 

 by differences in size and structure, which show them- 

 selves at its first appearance. It consists of a short, 

 tubular base, open at the top, to which a long spinous 

 process is articulated, which often attains a truly gigantic 

 size. It also takes on very commonly a peculiar form, 

 being broad and flattened, and bearing no slight resem- 

 blance to the blade of a scimitar. This, however, is not 

 universally the case, since, though always of remarkable 

 size, it seems sometimes to retain the cylindrical shape. 

 When fully developed, this sword-like appendage, bending 

 across the cell as if to guard the entrance, has a very 

 peculiar effect. 



Two of the spines, or sometimes four, are visible in 

 front of the ovicell. 



There can seldom be much difficulty in recognizing this 

 species. The characters of the area are amply sufficient 

 for identification, apart from the less stable and perma- 

 nent portions of the structure. 



When furnished with its full armature, M. Flem'mgii is 

 eminently picturesque and characteristic. 



MeMBRANIPORA CORNIGERA, Busk. 

 Plate XXI. fig. 4, and Plate XXII. fig. 3. 



Membhanipora CORNIGERA, Biisk, Eep. Brit. Assoc. 1859, Trans. Sect. 45 ; 



Quart. Journ. Micr. So. viii. (1860), 124, pi. xxv. fig. 2. 

 Membhanipora Flemingii, 1, forma cornigera, Smitt, CEfvers. K. Vet.-Akad. 



Forb. 1867, 367 and 403, pi. xxiv. fig. 1. 



