450 Mr. B. O. Bidley on Franz-Joseph-Land 



bearing some resemblance to an avicularian hollow. The 

 brown colour of the margin of the colony is evidently due 

 to the important part played by the chitinous part of the ecto- 

 cyst in the young cells, appearing as it does in the wide 

 fenestra of the front wall of the cell, the margin of the 

 mouth, &c. 



Porella concmna. Busk. 



Lepralia concinna, Busk, Cat. Brit. Mus. ii. p. 67, pi. xcix. 



Porella Icevis, Smitt, (Efv. Vet. Forh. 1867, Bihaag, pp. 21, 134, 217, 



pi. xxvi. figs. 117, 118. 

 Porella concinna, Hincks, Hist. Brit. Mar. Pol. p. 323, pi. xlvi. 



Several colonies. They agree with Busk's figs. 1, 3, 4, 5, 

 and the two cited figures of Smitt better than with any others 

 designed to represent this species. The marginal punctures 

 are constant. The cells are generally separated by a promi- 

 nent and undulating line. The inferiorly enlarged peristome 

 which encloses the avicularium is sometimes almost as pro- 

 minent as in P. struma, Hincks (Norman). In some young 

 cells a semilunar hollow in front of the mouth marks its future 

 position, showing that it owes its character to the avicularian 

 chamber which it contains, and which is afterwards perfected 

 by the extension over this hollow of the surrounding calca- 

 reous margin, just as the zooecium itself is formed by calcareous 

 growths from its margin. The avicularian chamber is liable 

 to become accidentally detached ; and then' it leaves a round 

 space below the mouth of the adult cell : this condition 

 appears to be represented by two of the upper cells of Busk's 

 fig.5(/.c.)._ 



A small circular incrusting colony is also referred, but with 

 doubt, to this species. It has an umbo immediately below 

 the lower lip, but apparently no avicularium there. The cells 

 are convex and distinguished from each other by their con- 

 vexity ; but there is no bounding line. No spines. The front 

 of the cell is covered, excepting the base of the umbo, with 

 coarse foramina. Cells slightly rhomboid. The intraoral den- 

 ticle is rectangular. No ooecia. 



A large spreading colony 24 millim. in extreme diameter is 

 apparently also referable to this protean species. On one side 

 the front of the cell is almost entirely occupied either by an 

 immense and very salient rostrum, in the oral side of which 

 lies the avicularium, or by a large depressed space, oblong or 

 semilunar, beneath which the wall of the cell is thin. The 

 cells with these spaces evidently constitute an earlier stage than 

 the rostrated cells ; and the rostrum, when it occurs, together 

 with its contained avicularium, is evidently developed over 



