GENERA OF FAVOSITID.E. 133 



equally thickened all round, so as to have their calices sur- 

 rounded by tumid margins of equal thickness, and mostly 

 rounded or subpolygonal in form. On the other hand, in Coenites 

 the thickening affects principally the upper aspects of the tubes ; 

 and hence the calices assume the form of long narrow slits or 

 fissures, the length of which greatly exceeds the width (PI. VI., 

 fig. 5). Lastly, in Pachypora there are usually numerous short 

 radiating septa, in the form of tubercles or spines. No struc- 

 tures, however, can be recognised in Ccenitcs as representing 

 the septa in the actual visceral chamber itself below the thick- 

 ened portions of the tubes ; and the only traces of these organs 

 are to be found in the tooth-like projections of the margins of 

 the calices. These projections are generally three in number 

 — two on one margin, and a single unpaired tooth opposite the 

 notch between these on the opposite margin ; but there may be 

 five of these teeth — three on one margin, and two on the other. 

 The tabulae present no specially noticeable features, being well 

 developed and complete, though not very numerous, through- 

 out the central unthickened portion of the tubes. The differ- 

 ent species of Ccenites will require careful revision, by the light 

 of microscopic sections, before they can be regarded as fully 

 established. 



In its geological range, the genus is principally Upper 

 Silurian ; but species supposed to belong to it have been also 

 described from the Devonian formation. In the Upper Silurian 

 rocks the genus is found in Britain, Europe, and North America. 

 The species which I have selected as illustrative of the genus 

 are Ccenites jtmtperinus, Eichw., and a form which I believe to 

 be the Ccenites linearis of Edwards and Haime. 



