216 



DB. W. D. LANG ON 



[vol. lxxiv, 



VII. MORPHASMOPORA JUKES-BROWXEI (Brydoiie) 



(figs. 11 & 12, pp. 216-17). 



An evolution has been followed from hypothetical primitive 

 forms through the comparatively simple Kelestoma and the more 

 complex Morphasmopora brydonei. And in its light the extremely 

 modified structures of M. jukes-broivnei may now be interpreted. 

 The intraterminal front- wall occupies only about the proximal half 

 of the cecium, and that part of it which is formed by the apertural 

 bar is nearly as big as the more proximal part formed of normal 

 costse. The costse are about ten in number, rather widelv spaced; 



Fig. 11. — Diagram of an cerium of Morphasmopora jukes -brown ei. 



X about 133 diameters. 



Ovicell. 



Lacuna in seccondary eircum- apertural 

 tissue. 



Aperture. 



Avieularium. 



Lacuna in secondary tissue intercalated be- 

 tween the avieularium and the proximal 

 apertural spine. 



A\ avy lacuna in secondary intercecial tissue. 



Proximal apertural spine. 

 Distal fork of apertural bar. 



Proximal fork of apertural bar. 

 Costa. 



but their pelmatidia liave retreated from the distal ends nearly to 

 half-way to the proximal ends, and the median area of fusion 

 occupies all the space between the pelmatidia — thus the intrater- 

 minal front-wall is considerably consolidated. The apertural bar is 

 greatly enlarged, each fork being wider than a normal costa. There 

 is a large, more or less diamond-shaped median space between the 

 fused forks on each side. The proximal pair of apertural spines is 

 even larger than in M. brydonei, and occupies as much room as the 

 apertural bar with its bifurcations. The fused distal forks of the 



