354 APPENDIX. 



In the fenestrate diAdsion^ in the whole of which the 

 cells are of larger size and stronger than in the other^ the 

 wall of the cell appears to be constituted of at least two 

 distinct laminae. The external lamina^ on the front of the 

 cell^ is perforated by a certain nnniber of holes, is wanting 

 rather in a certain number of spaces, for which spaces the 

 term " fenestrse^^ is employed. These apparent openings 

 do not, therefore, penetrate into the cavity of the cell. 

 But besides the fenestrse, there is, in some cases, a small 

 central opening which does penetrate through the wall. 

 In most cases the fenestrse are arranged in a crescentic, or 

 rather horse-shoe shaped line, indicative, as it were, of the 

 hmits of a regular oval space, in the front wall of the cell, 

 the upper part of which oval would be formed by the mouth, 

 and the remainder filled up by the deposition of cal- 

 careous matter, as happens for instance in the older cells 

 towards the bottom of the polyzoary in certain Cellula- 

 rise, &c. 



A further characteristic of the fenestrate Catenicellse is 

 the terminal position of the ovicells. These organs are 

 clearly transformed cells, or cells dilated to considerably 

 more than theii' natui-al bulk, and assuming a sub globose 

 form. And what is worthy of remark, these terminal 

 ovicells always have a sessile avicularium on the summit. 



In the " Yittatse" the cell is smaller, and usually more 

 delicate and transparent. They probably want the outer 

 lamina, or have it very thin, and consequently present 

 no fenestrate spaces, and the front of the cell is beset 

 (sometimes very sparingly) with more or less prominent, 

 minute, acuminate ^^papillse." On each side, sometimes 

 on the anterior aspect, sometimes quite laterally, is a 

 narrow elongated band or '^ ^dtta,'^ as it is here designated, 

 from which the distinctive sectional appellation is derived. 

 This band or stripe varies in width and proportionate 

 length and position in different species ; it is slightly ele- 

 vated, and marked with larger, or small circular discoid, or 



