155 



CHAPTER VII. 



Sub-geims Diplotrypa, Nich., 1879. 



(Pal. Tab. Cor., p. 312.) 



The corallum in the species included in this section is discoid, 

 sometimes globose, sometimes leaf-like, with a thin basal epi- 

 theca. The corallites are of two kinds, all of which have thin, 

 structureless, and apparently fused walls. The corallites are 

 mostly prismatic, but the larger ones may be oval {^M. calycula, 

 James). Spiniform corallites may be wholly wanting (as in 

 M. petropolitana, Pand.), or may be present in smaller or 

 larger numbers (as in M. Whiteavesii, Nich., and M. calycula, 

 James). There may be well-marked "monticules," formed of 

 the larger tubes ; but in general the large and small corallites 

 are uniformly intermingled. The tabulae in all the tubes are 

 complete, and those of the small corallites are more numerous 

 and more closely set than those of the large tubes. 



Dr Steinmann (N. Jahrb, fiir Min., &c., 18S0, p. 438) has ex- 

 pressed the opinion that the section of Monticuliporoids which 

 I have named Diplotrypa is properly identical with the earlier 

 Dianulites, Eichw. As has been seen previously (p. 11), 

 Diamilites, Eichw., is absolutely unrecognisable; and in express- 

 ing this opinion Dr Steinmann is doubtless to be understood as 

 referring to Dianiditcs, Eichw., as re-defined and emended by 

 Dybowski (Chsetetiden der Ostbaltischen Silurform., 1877). 

 Even, however, if I were to admit the desirability of the 

 attempt to revive an old and hopelessly ill-defined genus like 

 Dianulitcs, Eichw., I should find it impossible to accept as 



