158 



hypersloiiiial or eiulozocrcial, and in the latter case they are surrounded hy keno- 

 zoa'cia in the hitherto examined species. 



Tlie authors, who have liitherto set up genera witliin this section, liave chiefly 

 attached importance to the structure of the Iroutal shield, i. e. to the structure 

 of and the connection between the spines, of which it is composed. Here again 

 we must maintain, that on account of the vaiiable nature of the spines they are 

 but badly suited to alVord generic characters, and we must call attention to the 

 fact, that the difl'erent varieties, which Hincks lefers to (Irihriliiui iiunclaki, show 

 such great dillerences in the structure of the frontal shield, that some of them 

 cannot even be entered under his diagnosis of the genus Crihriliirci. I attach the 

 greatest importance to the same structures that I have made use of in dividing 

 the genera under Memhraniporidae. For want of material I must however here 

 confine myself to give diagnoses of the following 5 genera. 



Metnbraniporella Hincks, Char, emend. 

 Lepralia (Johnston) Norman '. 



The aperture in the frontal shield has an o[)ercular valve, and the shield is 

 perforated by slits. There are pore-chambers with few pores, and the hyperstom- 

 ial oa'cia are provided with an ectooti'cium but partially calcitied. Dependent 

 ouiciilaria may occur. 



This genus is here taken in a much more limited sense than by Hincks, and 

 with the exception of the presence of the frontal shield the two species, that we 

 have referred to it, correspond in ail characters with the genus Callopora and 

 show signs of being specially closely allied to C. Uiiinerili. Tliis appears for one 

 thing in the structure of the ooecia, the ectoooecium being in botli species only 

 calcified in its marginal portion. A frontal shield appears constantly in M. nilitla, 

 while tliis is not tlie case in an undescribed species from the Fa-roes. In the 

 latter we find in tlie same colony, besides a smaller number of zoa>cia with a 

 frontal shield, also some that are provided with but 2 — 4 distal, unconnected 

 spines. This species thus forms a link between Callopora and Memhraniporella. 



Cribrilina Gray. 

 Cribrilina Jull. p. p., Gephyrotes Norman 84, p. 100. 



(I'l. IX). 



The aperture in the frontal shield, which encloses an opercular valve, is usu- 

 ally provided with a more or less distinct proximal mucro. Pore-chambers with 

 few pores. The owcia are hyperstomial or enclosed by kenozoa'cia, and the wholly 



' 84, p. 100. 



