OF COENOPSAMMIA FROM LIFU. 359 



With the production of buds the base of the colony broadens. The parent and 

 daughter corallites continue to increase in height and size, daughter polyps being again 

 formed on their outer sides by budding from their free basal edge. The final result 

 is an incrusting mass with a number of corallites standing up separately upon it, the 

 oldest being tj'pically in the centre (Fig. 1). 



As the corallites ai'e built up, skeleton of a loose, porous nature — peritheca' — is 

 deposited between them by the extrathecal portions of their polyps. The different 

 corallites of a colony are hence only free for a limited height, the highest free portion 

 of any corallite in the collection being 12 mm., and the greatest diameter of the largest 

 corallite 9 mm. 



Hence, if growth proceeds regularly, a low convex mass is formed, the corallites 

 gradually decreasing in height and diameter fr(5m the centre outwards. The colonies 

 in the collection have this general form, but are all very small — largest 5.5 cm. 

 across (Fig. 1) — and rather irregular, being overgrown in places by foraminifera, sponges, 

 and other organisms. To the struggle between these and the polyps may be directly 

 ascribed in many places the variation in height of the corallites above the colony. 

 The mode of growth however of the species can be distinguished in all. 



The corallites have on the outside an appearance of longitudinal striae, due to 

 the presence of low, rough, subequal costae, which correspond in number and position 

 to primary, secondary, tertiary, and quaternary septa. Many of the costae are con- 

 tinuous from the parent to the daughter corallites in the young stage, but where 

 much peritheca has been formed there is a distinct narrow valley between the corallites, 

 from which the costae diverge. 



The theca is thin, and for a few millimetres below its upper edge very freely 

 perforated in lines between the costae (Fig. I.). It does not appear to be a true theca, 

 formed in the first place by the basal ectoderm as a ring on the basal plate, joining the 

 septa, but rather a pseudotheca, formed by the fusion of thickenings of the septal sides. 



The calice is slightly oval in shape, the two diameters being in the proportion 

 to one another of nine to eight. Within it septa of three cycles are present, of which 

 the primaries and secondaries fuse with the columella (Fig. 3). The primary septa 

 generally project from the edge of the calice almost horizontally inwards for about a 

 quarter of its diameter — they often in the younger corallites rise slightly above the level 

 of the theca— ending by the axial fossa with almost smooth vertical edges. The two 

 primary septa, which lie between the directive mesenteries at each end of the longer 

 diameter of the calice — hence termed directive septa — do not project for more than 

 about one-seventh the diameter, so that the axial fossa is very distinctly oval''. 



The secondary septa project horizontally from the upper edge of the calice for 

 about one-twelfth its diameter, ending then with almost vertical edges, but abruptly 

 broadening to join the columella. The tertiary septa are small and inconspicuous, and 

 the quaternary are low ridges, only seen in ground down surfaces or sections towards 

 the base of the calice. 



' For definition of this term see p. 301. 



« These proportions are not clearly shown in the figure, which has been somewliat diagrammatioally drawn 

 by the artist. 



49—2 



