PLATE X. 



All the figures in this Plate illustrate the structure of the different forms of Daclijlopora. 



Fig. 

 1 — 



18. 



19. 

 20. 



—Varietal forms o[ Dactylopora eruca, magnified 

 30 diameters, except Fig. 4 a, which is en- 

 larged to CO diameters. All these are from 

 recent specimens, except Figs. 4 and 8. 



9 — 14. — Varietal forms of Dactylojmra anmilus ; 

 40 diam. 



15. — Dactijlopora chjpelna, magnified 15 diameters; 

 A, small portion magnified 10 diameters. 



16. — Fragment o( Daclijlopora diyitata ; 15 diam. 



17. — Dactylopora reticulata; at a, magnified 15 dia- 

 meters, and at b, enlarged to 40 diameters ; 

 a a', juMctural interspaces, as seen externally; 

 b b', interior furrow, in which are seen the 

 internal entrances to the junctural interspaces; 

 c, c, outer walls of the chambers ; c c' , cavities 

 of the chambers laid open from the outside by 

 the attrition of their walls ; d, d, cavities of 

 the chambers laid open by vertical section ; e, 

 apertures of tlie chambers. 



Another variety of Dactylopora reticulata, showing 

 the outer wall of each annulus between the 

 junctural interspaces a a', strengthened with 

 projecting ribs : 40 diam. 



■The same viewed from above. 



Specimen of the simplest variety of Dactylopora 

 cylindracea, magnified 15 diameters; — a, por- 

 tion of its external surface, enlarged to 40 

 diameters; n, portion of its fractured edge, 

 enlarged to 40 diameters, showing the gallery 

 a a, into which the chambers of the chambered 

 portion b, b open. 



21. — Variety of Dactylopora reticulata, in which the 

 chambers are not arranged in regular annuli ; 

 thus leading towards D. (jlandulosa : 15 diam. 



23. — Portion of a specimen resembling that sho.vn in 

 Fig. 20, laid open by acid from its exterior, 

 so as to show the cavities of the cliamljers, of 

 which the internal orifices are seen at a, a, 

 and which are surrounded by passages diverg- 

 ing from the necks of those orifices, the cross 

 sections of which are seen at b, b : 40 diam. 



23. — Portion of a specimen of the more complex type 

 of Dactylopora cylindracea sliown in Fig. 29, 

 of which tlie external surface has been re- 

 moved by attrition : 15 diam. 



2 1. — Portion of a specimen oi Dactylopora cylindracea, 

 resembling that shown in Fig. 20, hut more 

 highly developed, showing at a' a' the gallery 

 formed by the coalescence of the junctural 

 interspaces, communicating internally with the 

 general cavity of the cylinders by a row of 

 orifices in nipple-shaped protuberances, and 



Fig. 



opening externally into the chambers, b, b, 

 which are laid open by vertical section ; around 

 the neck of each of these chambers there ori- 

 ginates a set of diverging branches, d, d, which 

 pass round the chamber to reach the ex- 

 ternal surface, where they open into its funnel- 

 shaped depressions seen in section at c, c, c, c. 

 At A the same parts are represented as seen 

 in a horizontally fractured surface ; its differ- 

 ence from Fig. 20 a consisting in the more 

 complete continuity of the internal gallery, 

 a, a, and in the development of a thick wall 

 of solid shell-substance on the outside of the 

 chambered portion b, b : 40 diam. 



25. — Portion of the edge of a fractured specimen of 

 Dactylopora glandulosa, showing at a, a, the 

 internal orifices of the chambers, and at b, li, 

 the junctural interspaces left between the pro- 

 jections of their external walls : 40 diam. 



26.- — Portion of the internal surface of a specimen of 

 Dactylopora glandulosa (the chambers of which 

 are much smaller than the average) showing at 

 a, a, the mam miliary protuberance in which 

 the orifices of the chambers are situated, and 

 at b, b, the junctural interspaces here narrowed 

 to pores : 40 diam. 



27, 28. — Portions of the external and internal surfaces 

 of the ordinary form o{ Dactylopora glandulosa ; 

 a, a, internal orifices of the chambers ; b, b, 

 junctural interspaces : 40 diam. 



29. — Portion of the most complex type of Dactylopora 

 cylindracea, as seen under various aspects : 

 a, a, cavities of the chambers laid open ; b, b, 

 junctural canals, opening into the general 

 cavity of the cylinder by the orifices c, c, c, c : 

 at d, d, are seen the dilated citls de sac of 

 the junctural canals, from which originate the 

 diverging branches, e, e, wliich run towards 

 the surface, where they terminate in the funnel- 

 shaped depressions shown at g, g ; in the 

 lower part of the figure the diverging branches 

 are seen in cross section at e , e , whilst at /, 

 the external sheath has been so far removed as 

 to lay open the cuts de sac of two of the prin- 

 cipal canals from which they originate : 30 

 diam. 



30. — Portion of the solid sheath of a specimen of the 

 same type of the preceding, which has been 

 subjected to the action of acid ; showing a 

 division by sutural lines into areola, in each of 

 which are seen the transverse sections of the 

 diverging branches of one of the junctural 

 canals : 40 diam. 



