266 



MINERALS AND GEOLOGY 



Modern bryozoa are generally divided into Entoprocta and Ecto- 

 procta, according as to whether the anal orifice is within or without 

 the tentacular area. The Entoprocta have no fossil representatives. 

 The Ectoprocta are subdivided into two leading sections : 1, Phylac- 

 toloemata, in which the mouth is furnished with a skin-like " epistome " 

 or moveable cover, and the " lophophore " or tentacle-bearing organ 

 is of horse-shoe form, as seen in the fresh-water genus Plumatella, 

 <fec.; and 2, Gymnolcemata, in which there is no epistome, and the 

 lophophore is circular in form. The first section or Order is supposed 

 to have no fossil representatives. The Gymnolozmata are divided 

 into four sub-Orders, two of which, Cyclostomata and Cheilostomata, 

 include fossil examples. Living forms of these sub-Orders are 

 exclusively marine types. In the Cyclostomata, the cells are tubular, 

 and the cell-opening is terminal and as large as the diameter of the 

 cell. The cyclostomes date from the lower Silurian period. The 

 delicate lace-like genera, Fenestella and Ptilo- 

 dictya, are common Canadian examples ; and 

 certain other forms ( ' Monticulipora, &c,) gen. 

 erally referred to the HYDRO-CORALLA, are also 

 placed under this Order by some palreontolo- 

 zists. In the Cheilostoma the cells are oval or 

 egg-shaped, and the cell-opening is narrower 

 than the general width of the cell. It is also 

 furnished in many forms with an articulated lid 

 or operculum. This sub-order is only known with certainty to date 

 from the Jurassic period : we have consequently no examples in 

 Centra] 



FIG. 181. 



Fenstella Etegans. 

 Upper Silurian. 



Hall. 



II. 

 BRACHIOPODA. 



The brachiopods are separately-living, marine, molluscoid animals, 

 provided with a bivalve shell. This latter character, and their gen- 

 eral aspect, causes them on superficial observation to seem very 

 nearly allied to the lamellibranchiates or ordinary bivalve mollusca, 

 but, rightly considered, they are far more closely connected with the 





