APPENDIX. 353 



he, is always distinctly separated by a septum from the 

 cavity of the avicularium itself. Below the avicularium 

 there is also iu many cases a third distinct cavity which is 

 usually widely open, the opening beiag covered ia very 

 frequently by a convex transparent membrane, and its bot- 

 tom apparently perforated by several minute foramina — 

 from this part of the lateral process there is in many spe- 

 cies a prominent ala or keel prolonged to the bottom 

 of the cell — which ala not unfrequently divides into two 

 branches, which, again coalesciag at the bottom of the cell, 

 circumscribe a more or less oval space, the bottom of 

 which is also perforated by miuute foramiua or apparent 

 foramina, and which is often covered over by a transparent 

 convex membrane. This membrane, however, as weU as 

 that which covers in thesubavicularian space, is more usually 

 broken off and wanting. 



The inferior oval space above described is here termed 

 the lateral area, and it is employed in the specific charac- 

 ters. It would thus be correct to say — that each cell is 

 furnished with two lateral processes, each of which in the 

 fully developed state consists of three distinct compart- 

 ments, — one superior, a cup or spine : a middle one, which 

 is the avicularium: and an inferior; and it would appear 

 that one or more of these elementary compartments of the 

 lateral process may be more developed than the next, or 

 sometimes entirely aborted. The mouth of the cell is 

 situated at the upper part in front, and is of the same con^ 

 formation as in the rest of the Cheilostomatous sub-order. 

 An important generic character consists in the gemiuation 

 of the cell at each bifurcation.* 



These characters are common to all the species included 

 in the genus, which furthermore admits of being subdivided 

 into two extremely natural sections or subgenera, (or per- 

 haps into three). These subdivisions are named respec. 

 tively the " fenestratse," and the " vittatse." 



VOL. I. 



Tab. I. fig. 1, 2. 

 



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