;300 R. jU. Brydone — Further Notes on the Trimmingham Chalk, 



with rounded basal angles, and stretches from side wall to side wall, 

 liut its apparent breadth is restricted by a very slight infold of the 

 inner edge of the side walls. The lower lip is almost straight, but 

 the very slight curve is often accentuated by the arching of the front 

 wall from side to side. The avicularium is an elongated cell with au 

 oval aperture occupying two-thirds of the area, and touching the cell- 

 walls at its widest, but separated from them above that point by 

 a very slight deep-seated front wall, and below that point by a con- 

 siderable front wall rising towards the foot of the cell to the plane of 

 ti)e top of the cell-wall. The species is very characteristic of the 

 upper part of the zone of B. qnadrata. 



CuiBRiLiNA Gregoryi, sp. uov. (Fig. 13.) 



Colony either adherent or free and unilamellate. Cells large, with 

 walls on the whole common, though often showing signs of separa- 

 tion. Aperture large and semicircular, surrounded by a broad 

 smooth border, which extends between the upper edge of the 

 aperture and the foot of the next cell for a distance equal to or 

 greater than the height of the aperture. From the upper part of this 

 band two prominent denticles project out over the aperture. The 

 front wall springs from slightly below the surface of the side walls, 

 and is gently arched. It bears about seven rows of punctures, 

 ruiniing straight across from side to side, the two punctures next the 

 side walls being much larger than the others. There are usually 

 two avicularia, always one, to each cell, closely associated with the 



. 'C'.V 



# 



Fig. 13. 

 lower corners of the band round the aperture. They are small and 

 mandibular, but except in well-preserved specimens from the zone of 

 Ji. quadrata, where this species reaches its zenith, the mandible is poorly 

 or not at all developed, and the avicularia present themselves as very 

 .small circular perforate denticles. No ovicell has yet been observed, 

 tiiough man}' thousands of specimens have been seen. The species 

 most nearly resembles Semiescharipora dentata, D'Orb. (which is, 

 however, near the JlemhraniporeUce) , but is easily distinguished from 

 that and all other species by the two imperforate denticles over- 

 hanging the aperture. It appears in tlie zone of M. cor-testtidinarhim 

 (at Seaford), and becomes steadily more prevalent until in the upper 

 part of the zone of B. quadrata it is the dominant form ; above the 

 base of the zone of B. mucronata it soon becomes comparatively rare. 



