316 TABULATE CORALS. 



The nearest ally of M. (Diplotrypa) petropolitana with which 

 I am acquainted is one of the forms which I previously de- 

 scribed as Chcetetes petropolitanus, from the Lower Silurian 

 rocks of North America. Now, however, that I know the 

 internal structure of the Russian species, I find that the 

 American specimens are specifically distinct, and I shall de- 

 scribe them under the name of M, (Diplotrypa) Whiteavesii. 

 They are distinguished from M. petropolitana, Pand., by the 

 much closer tabulation of the small corallites, the peculiar 

 double tabulation of many of the large corallites, and the 

 form and size of the latter tubes. From the forms which I 

 shall here describe under the names of M. (Monotrypa) un- 

 dulata, and M. (Monotrypa) Winteri, the present species is 

 easily distinguished on minute examination ; for both the 

 former types are destitute of a series of small corallites 

 interspersed among the ordinary tubes of the colony, while 

 all the corallites are similarly and uniformly tabulate. 



Formation and Locality. Lower Silurian (Chasmops Lime- 

 stone), Ostragothia, Sweden. Collected by Dr Lindstrom. 



Monticulipora (Diplotrypa) Whiteavesii, Nich. 

 (PI. XIIL, figs. 4-4 b, and PL XIV., fig. i.) 



Chatetes petropolitanus, Nicholson, Quart. Journ. Geol Soc., vol. xxx. p. 510, 



PI. XXX., figs. 5 - 8, 1875. 

 petropolitanus (pars), Nicholson, Pal. of Ohio, vol. ii. p. 204, PI. XXI., 



figs. 14, 14 b, 1875. 

 petropolitanus, Nicholson, Ann. Nat. Hist., ser. 4, vol. xviii. p. 88, PI. 



V., figs. 6, 6 a, 1876. 

 petropolitanus (pars), Nicholson, Geol. Mag. Dec. ii., vol. ii. p. 175, 



1875. 

 petropolitanus, Nicholson, Rep. Pal. of Ontario, p. 10, PI. IV., figs. 3 



and 4, 1875. 



Spec. Char. Corallum discoid when young, hemispheric 

 when adult, often with the lateral margins widely extended, 

 the base being usually deeply concave, sometimes flattened, 

 and being covered by a concentrically striated epithecal plate. 



