CYCLOSTOMATA. 



625 



attached, since thin sections prove the absolute continuity of the 

 substance of the two ; while the processes themselves consist, as 

 does the polyzoary from which they spring, of an external finely- 

 tubulated layer and an internal homogeneous stratum. The nature 

 and use of these singular appendages cannot at present be more 

 than guessed at. 



As regards the chief types of the FenestellidcB^ the genus Fenestella 

 itself ranges from the Silurian to the Permian inclusive, and comprises a 

 large number of species, the greater part of which belong to the Devonian 

 and Carboniferous rocks. In this genus (figs. 467, 468, and 469, C and 



in 



Fig. 469. — A, Poriferous side of Polypora rigida (Devonian) ; b, Non-poriferous side of the 

 same ; c and d, Poriferous and non-poriferous sides ol Fenestella biseriata (Devonian) ; E, Section 

 of Phyllopora sp. (Devonian), showing the anastomosing branches and the form and arrangement 

 of the cells ; f, Non-poriferous side of the same ; g, Transverse and vertical section of Car- 

 inopora Hindei (Devonian), showing the greatly developed keels, with the biserial cells at their 

 bases; h, Section of the same parallel with the poriferous face ; I, Part of the non-poriferous side 

 of the same. All the figures are enlarged. (Figs, a — d are after Hall ; e — i are original.) 



D), the polyzoary is fan-shaped or infundibuliform, the cells being de- 

 veloped on one side only, this being generally, if not always, the inner 

 side of the colony. The branches are straight, and are connected at 

 short intervals by regularly placed, non-poriferous cross-bars, or " dissepi- 

 ments." The zocecia are always biserial, the two rows of each branch 

 being separated by a median ridge or keel. In its general structure the 

 Devonian genus Carinopora (fig. 469, G — 1) resembles Fenestella, the poly- 

 zoary being funnel-shaped, with the cells opening on the inside, and each 

 branch having a double row of cells separated by a median keel. In this 

 genus, however, the keels on the branches are enormously developed, 

 and the external aspect of the polyzoary resembles that of Phyllopora. 

 The genus Semicosciniitm, also from the Devonian rocks, is considered 

 by Ulrich as identical with Carinopora, but in this case the zocecia open 



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