156 THE GENUS AIONTICULIPORA. 



its equivalent the modern Dianulites, Dyb. My reasons for 

 arriving at this conclusion have been previously stated (p. 

 21), and may be briefly summarised as follows: Diamilites, 

 Eichw., is entirely unrecognisable ; and there is therefore, in 

 the first place, a strong theoretic objection to its revival. In 

 the second place, Dianulites, Eichw. (emend. Dybowski), is 

 not a natural group, as it includes forms which unmistakably 

 differ from one another in their fundamental structure. In 

 the third place, Eichwald in his second definition of Dianulites 

 strongly insisted upon the presence of a " spongy coenen- 

 chyma" as one of the essential characters, whereas Dybowski 

 makes the absence of a "■ coenenchyma " a vital feature in his 

 definition of the same genus. Moreover, it is certain that in 

 some of the forms included by Dybowski under the head of 

 Diamtlites a " coenenchyma," though not a " spongy " one, is 

 present, or, in other words, there exist " interstitial corallites." 



I therefore retain the section Diplotrypa, Nich., and shall 

 elucidate its characters more fully in the description of the 

 following species : — 



Monticulipora (Diplotrypa) petropolitana. Pander. 



(Fig. 3°-) 



Favosiies peiropolitaniis, Pander, Russ. Reiche, p. 105, PI. I. figs. 6, 7, 10, 



II, 1830. 

 Diamdites petropolitauus. Dybowski, Die Chtetetiden, p. 24, PI. I. figs. 4 



and 5, 1877. Compare also D. fastigiatus, Eichw. (Dyb.), loc. cif., p. 



20, PI. I. figs. 1-3. 

 (Non C/icetetes petropolitajins, Nicholson, Quart. Journ. Geol. Soc, vol. xxx. 



p. 510, PI. XXX. figs. 5-8, 1874; Geol. Mag. Dec. ii., vol. ii. p. 175, 



1875 '} P^l- Ohio, vol. ii. p. 204, PL XXI. figs. 14-14/^, 1875 ; Ann. 



Nat. Hist., ser. 4, vol. xviii. p. 88, PI. V. figs. 6-6a.)^ 



Spec. Char. — Corallum discoid when young, but spheroidal, 

 or hemispherical when fully grown, the base being circular, 



^ Beyond pointing out that the forms which I have previously considered and 

 described as M. petropolitana, Pand., are really distinct from the original Russian 

 type of the species, I have not thought it — for reasons to be subsequently given — of 

 any use to attempt to give a synonymy of this form. 



