6l8 MOLLUSCOIDEA. 



have been referred by Mr Vine to the genus Diastoporella. The 

 foliaceous and erect forms of Diastopora are sometimes included 

 under the separate generic name of Mesenteripora, or, if consisting 

 of two layers of cells placed back to back, of Bidiastopora (fig. 460). 



Berenicea comprises forms which hardly appear to be separable 

 from Diastopora ; but the typical forms placed under this head con- 

 sist of crusts of superimposed cells. The genus has been quoted 

 from the Ordovician rocks, and there are numerous undoubted 

 Secondary, Tertiary, and Recent species. 



Also related to the Tubuliporidce is the family of the Entalophor- 

 idte, in which the polyzoary is erect and free, rising from an expanded 

 adherent base, and formed of long tubular cells which usually open 

 all round the stems. The genus Entalophora {Pustulopora) itself 

 ranges from the Jurassic to the present day, and has the cells open- 



Fig. 461. — Entalophora {Pustulopora) cellarioidcs, of the natural size and enlarged. Jurassic. 



ing irregularly on all sides of the branches. The name of Spiropora 

 is usually given to forms essentially similar to the preceding, but 

 having the cells so disposed that the cell-mouths form simple circles 

 or spirals round the stems. Species of Spiropora appear as early 

 as the Silurian period, and numerous Secondary and Tertiary types 

 are known, while the genus still survives. 



In the family of the Idmoneidcs, the polyzoary is erect, and almost 

 always more or less branched, the branches being usually round, 

 and sometimes anastomosing with one another. The tubular cells 

 open on one side only of the polyzoary. In the genus Idmonea 

 itself (fig. 457, j) the cells are disposed in transverse or oblique 

 rows on each side of the front faces of the branches, which are 

 divided mesially by an angulation or longitudinal keel. The genus 

 ranges from the Chalk to the present day. In the genus Hornera (fig. 

 457, k), again, the polyzoary is branched and sometimes reticulated, 

 the cells opening on one side of the branches only, their mouths 

 being commonly placed in somewhat rhomboidal spaces marked 

 out by wavy anastomosing ridges. Interstitial pores occur between 



