PLATE XXI. 



Fig. 1. — A massive weathered specimen of Stromatopora concentrica, Goldf., 

 from the Middle Devonian of Gerolstein, of the natural size. The specimen shows 

 excellently the growth of the ccenosteum in latilaminte, and is closely similar in 

 aspect to the original example of this species described and figured by Goldfuss. 



Fig. 2. — Portion of the skeleton-fibre of Stromatopora concentrica, Goldf., 

 enlarged about 40 times, showing the sieve-like and porous structure of the 

 fibre. The section is tangential, and taken from a specimen from the Middle 

 Devonian of Sotenich, in which the minute structure is unusually well preserved. 



Fig. 3. — Portion of the surface of a large specimen of Stromatopora concentrica, 

 Goldf., from the Middle Devonian of Gerolstein, enlarged about 3 times. 

 The specimen is traversed by minute " Caunopora-tubes," and the surface- 

 characters are unusually well shown. 



Fig. 4. — Upper side of a small specimen of Stromatopora typica, Rosen, from 

 the Wenlock Limestone of Ironbridge, of the natural size. 



Fig. 5. — Under side of the same, showing the epitheca, of the natural size. 



Fig. 6. — Profile view of the same, of the natural size. 



Fig. 7. — Part of the surface of the same, enlarged about 3 times. 



Fig. 8. — Sketch of a medium-sized specimen of Stromatopora typica, Rosen, 

 from the Wenlock Limestone of Dudley, of the natural size. The specimen has 

 been bisected, and shows the latilaminar mode of growth of the ccenosteum. 



Fig. 9. — Portion of the skeleton-fibre of another specimen of the same, from 

 the Wenlock Limestone of Ironbridge, enlarged about 40 times. The section is 

 tangential. 



Fig. 10. — Portion of a vertical section of the preceding, similarly enlarged. 



Fig. 11. — Part of the surface of a specimen of Stromatopora typica, Rosen, of 

 the natural size, in which the ccenosteum is traversed by numerous irregular 

 " Caunopora-tubes," which in this case seem to certainly belong to a species of 

 Aulopora. The specimen is from the Drift of Northern Germany, and was 

 presented to the author by Prof. Ferdinand Roemer. 



