Development of TctradiiiDi Cellulosiini Hall. — Ruedematin. 25 
served young corals (figs. 3 and 4). We have here, there- 
fore, relations similar to those found among the monticuli- 
poroids, where also certain forms possess a distinct dark med- 
ian line, while in others a perfect amalgamation has taken 
place. All these observations must teach that it cannot be a 
question of great systematic importance whether the walls of 
Tetradiinn are simple or double, and, that the separation of 
ChcBtetcs and Tetradinm into two families can hardly be 
founded on this. 
To sum up, it may be said that, in the writer's opinion, 
the nature of the interior processes, and of the walls, as well 
as the mode of growth of the coralla, proves at least this 
species of Tetmdmnt to be a chaetetide and that CJicetetes and 
Tetradinm are only genericall)' different. 
Explanation of Plate V. 
All figures represent sections of Tetradiwn cellulosiDii Hall, sp., from 
the Ordovician (Birdseye limestone, lower Trenton) of Ingharm's Mills, 
N. Y. ' 
Fig. I. — Young stage with beginning fission. Magnified 16 diam- 
eters. 
Fig. 2. — Stage with more advanced fission. X 16. 
Figs. 3 and 4. — Corallum after the first fission. X 16. 
Fig. 5. — Corallum with seven corallites, resulting from the fission of 
one of the corallites of the preceding stage. X 4. 
Figs. 6a and 6b. — Opposite sides of one section (2 mm. thick). Seen 
in reflected light. X 4. 
6a. — Fission of one corallite nearly completed. 
6b. — Fission of two corallites completed. 
Fig. 7. — Stage with completed fission of three corallites. X 4. 
Fig. 8. — Fission of all four corallites completed. X 4. 
Fig. 9.— Corallite with 4 primary and 8 secondary plications. X 16. 
F'ig. 10. — Corallite with nearly completed fission. X 16. 
Fig. II. — Beginning fission of a whole corallum. X 4. 
Fig. 12. — Complete fission of the same corallum. 12a cut obliquely. 
X 4- 
Fig. 13. — Beginning transversal fission. X 2. 
Fig. 14. — Longitudinal fission. X 2. 
Fig. 15. — Section through apparently intersecting bands of corallites. 
15c cut obliquely. X 4. 
Fig. 16. — Specimen showing structure of wall. X 8. 
Fig. i6a. — The same. Wall enlarged. X 125. 
