158 



hyperstomial or endozooecial, and in the latter case they are surrounded by keno- 

 zooecia in the hitherto examined species. 



The authors, who have hitherto set up genera within this section, have chiefly 

 attached importance to the structure of the frontal 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 variable nature of the spines they are 

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

 fact, that the different varieties, which Hincks refers to Cribrilina punctata, show 

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

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

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

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

 confine myself to give diagnoses of the following 5 genera. 



Membraniporella Hincks, Char, emend. 

 Lepralia (Johnston) Norman ^ 



The aperture in the frontal shield has an opercular valve, and the shield is 

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

 ial ooecia are provided with an ectoooecium but partially calcified. Dependent 

 auicularia 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 all characters with the genus Callopora and 

 show signs of being specially closely allied to C. Dumerili. This appears for one 

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

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

 while this is not the case in an undescribed species from the Faeroes. In the 

 latter we find in the same colony, besides a smaller number of zocecia 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 Membraniporella. 



Cribrilina Gray. 

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



(PI. 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 ooecia are hyperstomial or enclosed by kenozooecia, and the whollj' 



' 84, p. 100. 



