REFERENCES 367 



12. B. O. Ulrich : Journal of the Cincinnati Society of Natural History, vol- 



ume V, Cincinnati, 1882, pages 121 et seq. 



13. : Geological Survey of Illinois, volume viii, Springfield, 3800. 



14. : Geological Survey of Minnesota, volume iii, part i, Miimeapolis, 



1893. 



15. E. B. Wilson : Philosophical Transactions of the Royal Society of London, 



volume 174, part iii, London, 1884, pages 723-815. 



Explanation of Plates ^ 



Plate 19. — Development of the Monticuliporoids 



Figures 1-6. — Transverse serial Sections of a Colony of Prasopora conoidca 

 Ulr. 



Figure 1 is the finished section, and is at the level indicated by the line 

 r-r', figure 20. Figure 4 is about the level p-p', figure 20, and figure 5 is 

 at the level n-ii', figure 20. Figure G is slightly higher. These figures are 

 selected from a set of 18 drawings, representing 18 successive levels be- 

 tween 7'-?'' and m-m', figure 20. A section at the level m-m' is similar in 

 all essential respects to figure 31. Figures 3 and 4 show how the buds e 

 and f swing in toward each other, and thus come to rest on the protoecium, 

 which lies beneath the point marked o. All figures X 43. (106-10.) 



Figure 7.^^/1 (Ictailcd Drawinff of a transverse Section ihroii(/h the initial 

 Refjion of Callopora dalei (M.-E. and H.). 



Showing the protoecium and the ancestrula. A slight constriction be- 

 tween the two will be noted. This constriction is not observed on the 

 upper surface of the specimen— that is, if the slide be turned over and the 

 microscope accurately focused on the upper surface of the section the 

 walls of the ancestrula and protoecium will be seen to be continuous. 

 X 43. Cut No. Y, Tanner's cr. Mount Hope formation. (118-3.) 



Figure 8. — Transverse Section of the Protoecium of another Specimen of 

 Callopora dalei. 



The lateral buds come off on the under side of the ancestrula, well back 

 toward the protoecium, as in recent TahuHpora (cf. figure 30). X 43. 

 Cut No. V, Tanner's cr. Mount Hope beds. (118-11.) 



3 All drawings except figures 10, 11, 12, 13, 28, and .30 were made with the camera 

 Incida. Figures 10, 28, and 30 are after Barrois and figixres 11 and 12 after Beecher. 

 Figures 32-41 are microphotographs of the original sections. 



Letters and numerals having the same meaning for all the figures : 



a, J), c, 0, e, f, buds of the second or third generation. 



z-z', buds probably of the second generation, from which the buds c and f are sup- 

 posed to be derived. 



A, Ancestrula. 



0, Protoecium. 



x-x'. Thickened wall of the ancestrula and primary buds. 



1, Median primary bud. 



2, Left lateral primary bud. 



3, Right lateral primary bud. (These numbers do not apply to figures 11 and 12.) 



