GENERA OF CH.ETETID.E AND MONTICUIJPORID.E. 263 



rarely (C hyperboreus, Nich. and Eth., jun.) forming thin flat- 

 tened expansions, with a concentrically-striated epitheca below. 

 The corallites are irregularly polygonal, and are in complete 

 contact throughout their entire length. Rough fractures (gen- 

 erally, but not always) expose the interior of the tubes ; and 

 thin sections, whether transverse or longitudinal (PI. XII., figs. 

 4, 4 a, 4. d), show that the walls of contiguous corallites are 

 entirely and undistinguishably amalgamated or fused with one 

 another, the originally duplex character of the partition between 

 neighbouring corallites being in no case recognisable. Though 

 somewhat variable in shape and size, the corallites are indubi- 

 tably of one kind only, and there is no reason for believing that 

 the corallum consisted of two distinct sets of zooids. The 

 corallites, further, are not reclined, as in the typical species of 

 Alveolites, Lam., but are erect, in precisely the sense that this 

 term is employed in speaking of the massive coralla of species 

 oi Favo sites, such as F. Gothlandica, Lam., and its allies. The 

 calices, therefore, though wanting the regularly polygonal form 

 of those of Favosites, are never oblique or semilunar, with one 

 lip more prominent than the other, as is so characteristically 

 the case in Alveolites and its allies. The walls of the corallites 

 seem to be wholly imperforate, and as this conclusion is based 

 upon a minute examination of thin sections as well as of actual 

 specimens, its correctness may be accepted as tolerably certain. 

 This character, therefore, alone is sufficient to separate Chcetetes 

 from all the externally similar genera of the Favositidce. No 

 traces whatever either of lamellar or of spiniform septa can be 

 detected in thin sections or in the specimens themselves (except 

 some obscure longitudinal striae in C. scptostts\ and these struc- 

 tures must therefore be considered as wholly wanting. There 

 exists, however, in a certain number of the corallites a curious in- 

 ward projection of the wall (PI. XII., figs. 4, 4(5), which is seen 

 both in typical specimens of C. radians, Fischer, and also in C. 

 hype7^boreus, Nich. and Eth., jun., C. {Alveolites) scptosns, Flem., 

 and C. {Alveolites) dcpressus, Flem. In the two last-mentioned 

 species this inward process was noticed and figured by Edwards 



