498 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



this genus in this country are the three mentioned by Miller in his North 

 American Geology and Paleontology, viz: P. devoniense, P. woodmani, and 

 P. solitarhim. The last mentioned of these can scarcely be referred to the 

 genus Pachyphyllum, since it is described as a simple coral with an epitheca 

 (or theca) and without exothecal tissue. Pachyphyllum woodmani was 

 originally mentioned by White as Smithia woodmani. 1 Hall and Whitfield 

 describe and figure it 2 under the name of Pachyphyllum woodmani, saying 

 "the exsert form of the cells, and their limitation by an outer wall, are 

 features which do not exist in Smithia, but pertain to the genus Pachyphyl- 

 lum." In point of fact, Pachyphyllum seems to be a synonym of Smithia. 

 The genus is characterized by Edwards and Haime as follows: "Corallum 

 compound, increasing by lateral gemmation. Corallites not separated by 

 an individual epitheca, but united in their lower portion by a large develop- 

 ment of cost* and exothecal tissue; septa and tabula? well developed. 

 Pachyphyllum is distinguished from all other Cyathophylloids by the 

 development of the costse and exothecal tissue." 3 The description of 

 P. bouchardi, the type (ibid.), accords with the generic description, but, 

 unfortunately, by some oversight, it was not figured by the authors. 

 Although there is the usual reference heading the specific description, there 

 is no corresponding plate or description of plate in the accompanying atlas. 

 I am not aware that it has subsequently been figured. Smithia is described 

 by the same authors in the following terms: "Corallum compound, astrei- 

 form, multiplying by submarginal gemmation. Corallites intimately 

 connected, having the same structure as Acervularia (i. e., with two walls; 

 septocostal structure well developed between the walls; much less in the 

 central area. No columella. Tabulae little developed), except that they 

 lack external walls and that the septocostal rays are more or less confluent. 

 No columella," (Loc cit., p. 142.) 



A comparison of the two genera shows that they are at least very 

 closely related. One great distinction, implied rather than expressed, is 

 that in Smithia the one wall is regarded as homologous with the inner 

 wall of Acervularia, the intercellular tissue being then simply confluent 

 intermural tissue of adjacent cells. In Pachyphyllum, on the other hand, 



1 Geol. Rept. Iowa, 1870, Vol. I, p. 188. 



2 Twenty-third Aun. Kept. New York State Cab. Nat. Hist., p. 231, PI. IX, fig. 9. 



3 Hist. Nat. des Coralliaires, Vol. Ill, Paris, 1857, p. 391. 



