2IO TABULATE CORALS. 



with the hollow transverse floors which connect the corallites 

 in Chojiostegites Clappi, and into which the subvesicular tabulae 

 are similarly extended. The number of the connecting-pro- 

 cesses in the dififerent species of Syringopora is very variable. 

 Usually they are placed at tolerably distant and to some extent 

 regular intervals ; sometimes they are arranged in whorls {S. 

 verticillata, Goldf.) ; sometimes they are greatly reduced in 

 number {S. se7^pens^ Linn.) ; and sometimes they are given off 

 in verticils at corresponding levels, and coalesce so as to form 

 almost uninterrupted horizontal floors {S. tabulata, Van Cleve). 

 In .S". nobilis, Bill., and ^. intermedia^ Nich., both from the 

 Devonian of North America, the erect tubes throw out lateral 

 buds at short intervals, but the corallites are very rarely con- 

 nected by horizontal processes ; and it is possibly the case that 

 these forms should be regarded as a distinct subgeneric type. 

 Lastly, in the singular ►S. laxata, Billings, also from the 

 Devonian of North America, the connecting - processes are 

 totally wanting, and the corallites are for the most part quite 

 free. In places, however, the flexuous and closely-set tubes 

 come into partial contact, and at these points they become 

 coalescent by their walls. That their visceral chambers com- 

 municate directly at these points of partial coalescence, I think 

 hardly doubtful, though the preservation of my specimens will 

 not allow me to verify this conjecture. 



How far the arrangement and form of the connecting- tubes, 

 and the distances by which the various corallites in a colony 

 are separated from one another, can be employed as characters 

 of specific value, remains for future consideration. All that can 

 safely be said at present is, that too much stress has probably 

 been laid by the older observers upon these characters, and 

 that they must in reality be admitted to enjoy a considerable 

 variability within the limits of the same species, though they 

 exhibit at the same time a certain average condition, which is 

 by no means without its value, in each specific type. 



As regards the internal structure of the corallites of Syringo- 

 pora, we have only to notice the condition of the tabulae and 

 the septa. The tabulae (fig. 30) are typically, if not always. 



