The Quarterly journal of the Geological Society of London . l pair of apertural spines iseven larger than in M. bn/donei, and occupies as much room as theapertural bar with its bifurcations. The fused distal forks of the part 3] THE 217 apertural bar fuse with the apertural spines ; but proximally thereis a deep cleft between the apertural spines and the apertural circum-apertural avicularia are not so highly raised as inM. brydonei, are blunter in shape, more widely separated, anddirected proximally and towards the mid-line of the aperture whichthey accompany; and the pa
The Quarterly journal of the Geological Society of London . l pair of apertural spines iseven larger than in M. bn/donei, and occupies as much room as theapertural bar with its bifurcations. The fused distal forks of the part 3] THE 217 apertural bar fuse with the apertural spines ; but proximally thereis a deep cleft between the apertural spines and the apertural circum-apertural avicularia are not so highly raised as inM. brydonei, are blunter in shape, more widely separated, anddirected proximally and towards the mid-line of the aperture whichthey accompany; and the patch of interoecial tissue that was inter-calated in M. brydonei between the avicularium and the proximalapertural spine on each side is extended to meet its fellow patchacross the distal ends of the apertural spines, so that the proximaledge of the secondary aperture is formed of this strip of secondarytissue with its long, tongue-shaped, median lacunae. Distal to the Fig. 12.—Diagram of ancestrcecium o/Morphasmoporajukes-brownei. X about 175 Distal apertural spines. Aperture. Proximal apertural spine. Distal fork of spertural bar. Proximal fork of apertural bar. Extraterminal front-wall. avicularia the distal edge of the secondary aperture is bounded,as in M. brydonei, by two strips of secondary tissue meetingin the mid-line, each containing a long, somewhat triangularlacuna, so that each bears some resemblance to a much-elongatedavicularium. The interoecial secondary tissue has long, sinuouslacunae. A comparison of fig. 11 (p. 216), representing the ephebasticJHorphasmopora jukes-brownei, with fig. 2 (p. 207), representingthe hypothetical Primitive Kelestomine, shows the extent to whichmodification is carried in the former. .218 DR. W. D. LANG OX [vol. lxxiv, VIII. The Ancestrcecium of Morphasmopora jukes-browsei (fig. 12, p. 217). It is fortunate that the ancestroeeiimi of Morphasmopora juhes-brownei should have been preserved in one of the s
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