STEGANOPORELLA SMITTIT, 179 



latter to Miclieliu's Eschara Andegavensis. His figure 

 exhibits none of the peculiarities of the present species, 

 and is more probably, I think, a representation of the 

 common INIccliterranean form (also found in Tertiary de- 

 posits), which has been described under various names, 

 but was first characterized by Moll as E. impressa. 



The zocEcia are subquadrate, the opposite walls being 

 almost parallel. The front wall is somewhat depressed 

 below, but rises rather abruptly towards the inferior 

 margin of the orifice. On each side of its elevated por- 

 tion, which marks the course of the tubular entrance to 

 the inner chamber, are placed the foramina. They are 

 sometimes met with overspread with a delicate membrane, 

 and are not unfrequently obliterated by age and the pro- 

 gress of calcification. They open into the space lying 

 between the outer walls and the tubular neck of the 

 chamber. 



On the Cornish specimen the very curious avicularia 

 are present in great numbers, and, from their size and 

 the dark colour of the mandible, are very conspicuous ob- 

 jects. The area on which they are placed is large, almost 

 equalling in size that of the cells. It narrows off to a 

 point below ; and about the middle the aperture is con- 

 tracted by a projection of the margin on each side, which 

 bends over it, forming with the arched top of the area a 

 kind of frame round the mandible. The latter is flat, and 

 is traversed for about two thirds of its length by a narrow 

 band or rib, which is formed of stronger material than the 

 rest. In Mr. Busk^s type specimen from the Crag the 

 avicularia are also numerous ; and in two cases the man- 

 dible has been preserved, showing very cleai'ly the charac- 

 teristic structure which I have just described. 



The ovicell is of unusual size, and exhibits a curious 

 peculiarity in the horny lid which closes the large arched 



n2 



