POLYZOA OR BRYOZOA. 431 



open on all sides of the branches (fig. 271). The genus 

 extends from the Cretaceous to the Eecent period. The 

 family of the Tubuliporidce includes a number of well-known 

 forms, in which the tubular cells of the polyzoary are more 

 or less largely free and disconnected. In the genus Tiibuli- 

 pora (fig. 269, G) the tubes are free for a great part of their 

 length, and the colony is attached more or less extensively 

 by its base, the cells radiating from an excentric point. The 

 genus seems to extend from the Cretaceous to the present 

 day. Aledo (fig. 268, A) is very like the preceding, but the 

 ccencecium is creeping and irregularly branched, and the cells 

 are only free close to their mouths, and do not ascend as in 

 Tubulipora. The best-known forms of this genus are Tertiary 

 and Eecent, but examples which appear to be clearly refer- 

 able to it are found in deposits as old as the Lower Silurian. 

 Mesenteripora (Eidiastopora), again, resembles Alecto, but the 

 coenoecium is foliaceous, and the cells are in two layers, 

 separated by a calcareous membrane and opening on both 

 surfaces. 



Fig. 272. Mesenteripora (Bidiastopora) cervicornis, natural size and enlarged Jurassic. 



Closely allied to the Tubuliporidce is the great family of 

 the Diastoporidce, chiefly distinguishable from the preceding 

 by the fact that the tubular cells are not free even at their 

 terminal portions. In this group the genus Tubulipora of 

 the preceding is represented by Diastopora (fig. 269, H), in 

 which the encrusting coenoecium is discoidal, and more or 

 less excentric in its mode of growth. The Ceramopora of the 

 Silurian and Devonian (fig. 268, B), as before noted, is related 

 to Diastopora in many respects. Patinella (ranging from 



