POLYZOA OR BRYOZOA. 433 



calcareous lid, which is usually perforated in the centre. In 

 the course of growth a number of these hymen-like dia- 

 phragms may be formed in each of the interstitial canals, and 

 these tubes may thus come to be crossed by a succession of 

 perforated transverse partitions, which look like the "tabulae" 

 of the " Tabulate Corals." No such partitions, however, are 

 ever found in the larger tubes, which are regarded as the 

 true " cells." Heteroporella agrees with Heteropora in essen- 

 tials, but forms crusts upon foreign bodies. 



We have dwelt at some length on the structure of Hetero- 

 pora, as it has an important bearing upon the question as 

 to the true affinities and systematic position of certain of 

 the so-called " Tabulate " corals (such as Chcetetes, Fistuli- 

 pora, &c.) The general resemblance between specimens of 

 Heteropora and certain species of Chcetetes is undoubtedly 

 very striking ; and it seems quite probable that some of the 

 forms which have been described under the generic names 

 of Chcetetes, Monticulipora, Callopora, &c., may really prove to 

 be related to Heteropora, or to Heteroporella. The typical 

 forms of the above-mentioned Palaeozoic genera invariably, 

 however, possess complete transverse partitions or " tabulae " 

 crossing both the larger and smaller tubes (when both sets 

 of tubes are present). In spite, therefore, of the general 

 resemblance between them, we are at present hardly justified 

 in asserting that these types have any actual relationship 

 with Heteropora. 



The last family of the Cyclostomatous Polyzoa which needs 



Fig. 273. Fascicularia (Meandropora) cerebriformis. Tertiary. 



to be mentioned is that of the Theonoidce, comprising massive, 

 globose, or irregular forms, in which the cell-tubes are con- 

 tiguous and crowded together. The two principal genera 

 VOL. I. 2 E 



