CRIBRILINA RADIATA. 189 



They rise up occasionally into erect spinous processes. The 

 interstitial pores are either very distinct [radiata form), 

 or almost obliterated (innominata form). The small 

 vibraculoid appendages are often wanting. In the avicu- 

 larium there is a considerable amount of variability. In 

 some cases it is much more elongate than in others, and 

 much more elevated. In a specimen from the Red Sea (?) 

 it is of unusual length, rather blunt at the extremity, and 

 almost pedunculate. In British examples it is usually 

 shorter and broader. A more remarkable modification 

 occurs in a specimen of the radiata type from Madeira, 

 in which the avicularium is developed on the upper part of 

 a distinct cell, of much smaller size than the ordinary 

 zooecia^ but still well marked ; the beak is very short, pro- 

 jecting slightly beyond the top of the cell ; the mandible 

 is broad at the base, but becomes suddenly attenuated, and 

 tapers off to the extremity. 



This form may be regarded as less completely differen- 

 tiated than that which is commonly met with, in which 

 the avicularian cell is all but aborted, and little is to be 

 seen but the beak and mandible. These differences are 

 clearly of no specific value ; but they are interesting as 

 showing us what an unstable element of structure the 

 avicularium is. 



It may be mentioned here, that in this species there 

 are a number of large oval foramina round the base of the 

 cells, which are very conspicuous in those that are placed 

 on the edge of the colony. 



Habitat. At low-water mark, and on stones, shells, zoo- 

 phytes, &c. from moderate depths to deep water (175 

 fathoms) . 



Localities. Abundant on the south and south-west 

 coasts of England, ranging to the Isle of Man, west coast 

 of Scotland, Hebrides (the Minch), and Shetland, where. 



