Yol. 56.] AND CAMPTONITIC DYKES IN BKITISH EAST AFRICA. 229 



bearing shales. The coral occurred in a compact grey limestone. 

 The exposed parts of the fossil are marked by patches of white 

 calcite breaking in cleavage-rhombs, but one section shows enough 

 of the septa for the genus to be provisionally determined. 



The corallites are cylindrical in section, and the largest is about 

 10 mm. in diameter ; they are laterally free, but, judging from their 

 position in the specimen, they appear to be part of a csespitose 

 coral. The wall is thin, and the costae are prominent. The septa 

 are about 48 in number: that is, there are five complete orders. 

 The members of the first three orders are long, thin, and subequal ; 

 those of the 4th and 5th orders are shorter and also subequal. There 

 is a large trabecular columella. There is no sign of a fossula or of 

 pali, or of tetrameral symmetry. The affinities of the coral are 

 accordingly with Aplophyllia ; it will be noted, however, that there 

 is no conclusive proof from this small specimen of a csespitose habit. 

 It is conceivable that the corallites, instead of being part of an arbo- 

 rescent colony, may be simple and only accidentally associated ; yet 

 this is improbable. 



The specimen may be provisionally determined as an Aplophyllia 

 (syn. BhabdopliylUa), and compared with A. cervina, Etienne, from 

 the Oxfordian of Switzerland. 1 



EXPLANATION OF PLATE XII {pars). 

 Microscopic sections of igneous rocks from Mount Jombo. 



Fig. 3. Nepheline-syenite (No. G. 925, p. 224). The dark patch consists of 

 segyrine. with included crystals of sphene : below is a large Carlsbad 

 twin of felspar, and on the right a large plate of nepheline. X 12. 



4. Camptonitic dyke-rock (No. G. 923, pp. 224-25). The dark phenocrysts 



are partly basaltic hornblende (as, tor instance, the two large crystals 

 at the top on the left) and partly pale green augite (as, for example, 

 the large crystal in the centre and that at the top on the right). A 

 few small diamond-shaped crystals are sphene. The colourless pheno- 

 crysts are felspar. At the top, both on the right and on the left, are 

 patches of analcite. X 12. 



5. Segregation-patch in camptonitic dyke-rock (No. G. 921, p. 225). The 



section shows needles of deep-brown basaltic hornblende and pale 

 green augite, with a little sphene, in a base consisting mainly of 

 analcite. 



1 Koby, 'Monogr. Polyp, jur. Suisse' Mem. Soc. Pal. Suisse, vol. xi (1884) 

 p. 191 & pi. lvi, figs. 3-7. 



