2i() MYRIOZOID^E. 



specific distinction can be founded on so unstable an 

 element. As to sculpture, the puncta are generally absent 

 on the deep-water form, being obliterated by the dense 

 crust which involves the surface; but traces of them 

 may almost always be met with on the young marginal 

 cells. 



The avicularia are sometimes present on both sides of 

 the cell, frequently on one side only ; and in many cases 

 they are wanting altogether. They also vary slightly in 

 position, as I have pointed out in the diagnosis of the 

 species. Besides the oral avicularia, there are occasion- 

 ally others, irregularly placed. Sometimes one is de- 

 veloped at the bottom of the cell, with the mandible 

 pointing downwards or sideways ; and I have seen one on 

 each side of the mucro, a little below the aperture. The 

 species seems to be very liable to " sports." Occasion- 

 ally the surface of the cell presents a very singular 

 appearance, being studded with umbonate processes of 

 various shapes and sizes (Plate XXXI. fig. 4). The usual 

 mucro is now largely developed, so as to form a prominent 

 spike, and now, especially in the deep-water variety, al- 

 most abortive. 



I have also met with another very remarkable lusus. On 

 a specimen from deep water, a cell has the ovicell developed 

 below the mouth and reversed, so that the aperture faces 

 towards the lower margin. In several instances, too, on 

 the same specimen, a second ovicell occurs on the cell, at 

 one side, so placed as to cover, or partially cover, one of 

 the lateral avicularia. This monstrosity is of peculiar in- 

 terest, inasmuch as the growth of an ovicell immediately 

 above and overarching the avicularium is an indication of 

 the morphological significance of this structure, as a modi- 

 fied zooecium. 



HABITAT. On rock and under stones and on Lnmiimria 



