i68 



CHAPTER Vlli. 



Sub-genus Monotrypa, NIch., 1879. 



(Pal. Tab. Cor., p. 320.) 



The section Monotrypa, Nich., includes those species of Mon- 

 tictdipora proper in which the internal structure of all the 

 corallites of the colony is the same. The size of the corallites 

 may be uniformly the same, or there may be clusters of tubes 

 slightly larger than the average, which may be elevated above 

 the surface to form low " monticules." The internal struc- 

 ture of the large corallites (if present) is, however, the same 

 as that of the average tubes. Closely tabulate interstitial 

 corallites, also, are never developed. Spiniform corallites 

 are usually absent, but may be present {e,g., M. discoidea, 

 James). The walls are in some cases {e.g., M. 2tndulata, 

 Nich., M. Winteri, Nich., M. iin^egulains, Ulrich, &c.) thin, 

 seemingly structureless, and apparently amalgamated with one 

 another. In other cases {e.g., M. petasiformis, Nich., M. pul- 

 chella, E. and H., ]\L discoidea, James, ]\I. pavonia, D'Orb., 

 &c.), the walls of the corallites are appreciably, or even con- 

 siderably, thickened ; but they always preserve in such cases 

 the original lines of demarcation separating adjoining tubes. 

 The tabiUcE are always complete, and are uniformly distributed ; 

 but they are always comparatively few in number, and they are 

 sometimes almost wanting {e.g.,M. irregula^'-is, Ulrich). Type 

 of the group, M. utidulata, Nich. 



The above diagnosis is in several important points emended 

 and altered, as compared with that which I originally gave 



