123 



creature is at present unknown. Tlie similarity between the 

 cells of this species and the CcUularia avicularia is so very 

 great, that many naturalists have considered them the youn'' 

 and adult state of the same species ; and for this, or some other 

 reason, Dr. Fleming in his " British Animals" ranks them as 

 one ; he refers his F. avicularis to the Crista avicularia and 

 C. flnslroidcs of Lamouroux ; and the Scrtularia avicularia 

 of Linnaeus ; this cannot now however, be niainlained. As 

 the ceils in C. avicularia are only in two alternate rows, 

 ■while the Flustra. avicularis has about four or live, the ce/- 

 lularia is supposed to be the youngest state. In answer to 

 this, it may be observed, that the Flustra avicularis has been 

 obtained only one fourth of an inch in height, yet having the 

 four and five rows of cells ; while the Cellularia avicularia 

 Las not been found so small, but almost always higher than 

 the Flustra, and sometimes one third as high again with only 

 two rows of cells; and they have not yet been found in 

 company with each other. In addition to this, the Flustra 

 is common, while the other is comparatively rare ; and in 

 death the Flustra changes to a brown, while the other fades 

 to a dull white ; so that there can be no doubt of their being' 

 distinct. This opinion is also entertained by Johnston, 

 Milne Edwards, and Mr. Bean. 



* * * Crustaceous 



CHAGRIN SEA-MAT. F. Memhranacea. Encrusting; 

 cells quadrangular, alternate, with a blunt spine at each 

 angle. 



Flustra memhranacea, Ellis and Solander's Zooph., p. 18, 

 no. 12. Turton's Lin., vol. 4, p. 605. Fleming's Brit. An., 

 p. 536. Stewart's Elem., vol. 2, p. 437. Johnston's Brit. 

 Zooph., p. 287, pi. 38, fig. I, 2, 3. 



Hab. On sea weed, ( Laminaria digitata) every where 

 common. PI. xxi. 



This abundant species, encrusts the broad fronds of the 

 larger sea weed, in spots varying from a mere speck to two 

 or three feet in lengtii. It has a very delicate and gauze-like 

 appearance, and while lying exposed on the shore looks more 

 like a thin saline incrustation, than a living being. On ex- 

 amination even with the naked eye, it will be found to be 

 composed of quadrangular cells, with a blunt horn on each 

 angle. The longest diameter of the cell is in the axis of 

 growth, and the rims only are calcareously white; the other 

 portions being white and translucent. On the upper or distal 

 part of the cell, and but a very short distance from the two 

 spines, is a small semi-lunar opening, convex above and 



