312 ESCHARID^. 



bounded by a raised line, are occasionally present in 

 considerable numbers, but are sometimes altogether 

 absent. Ooecia roundedj sometimes almost immersed, 

 sometimes suberect ; a depressed area on the front, less 

 strongly calcified than the rest of the surface, inclosed 

 by a raised line, which takes the form of an arch ; at 

 the top of this area a transversely elliptical orifice closed 

 in by a membrane. 

 Colour, when fresh, bright red. 



Range of Variation. There are very considerable difffer- 

 ences in the elevation and convexity of the cells ; in 

 some cases they are much raised and have a mamillated 

 appearance. According to Smitt the umbo is sometimes 

 wanting ; but generally it is a very prominent feature, 

 rising at times into a spiked process. The punctures 

 seem to be commonly confined to the base of the cell, 

 where they form a single line ; but I have seen them 

 spreading over the entire surface. This seems, however, to 

 be of very rare occurrence. The surface is sometimes 

 smooth, but more generally roughened, and is very com- 

 monly striated by furrows passing upwards from the 

 margin. 



The oval avicularia are extremely irregular in their 

 occurrence, and when present are only developed here 

 and there over the colony. They are not noticed by 

 Busk in his account of the Crag specimens, nor can I 

 find them on that from the Devon coast; but on the 

 Guernsey and Floridan specimens they are present. 



The large pointed avicularia, each placed on a definite 

 area as large as that of the zooecia^ are extremely rare on 

 the British examples which I have seen. I believe I have 

 detected one or two of them by diligent search ; but on 

 the Floridan form figured by Smitt they are numerous, 



