26 NEW YORK STATE MUSEUM 



similarity in mode of growth, admitting however three different modifica- 

 tions in their structure. In the first of these, consisting exclusively of Siluric 

 forms, the demarcation of the outer and inner area is very obscure, and the 

 septa reach to the center of the cells ; in the second the septa are confined 

 to a narrow outer zone, and the zones are not separated by an intermediate 

 wall ; and the third has a distinct secondary wall separating the inner and 

 outer zones, and this the septa never transgress. Diplophyllum caes- 

 p i t o s u m, by the development of the septa which reach the center, falls 

 under the first group ; the second is that comprised under the generic term 

 Diphyphyllum ; and the third is equivalent to Eridophyllum. The last two 

 genera have usually been recognized by European writers, and Freeh has 

 stated that Diphyphyllum was based on corals of the Carboniferous lime- 

 stone, quite distinct from Eridophyllum, and a question may therefore arise 

 as to the propriety of employing the term Diphyphyllum so as to include 

 Diplophyllum. 



Diphyphyllum has been considerably misunderstood. Edwards and 

 Haime 1 united it with Lithostrotion, at the same time creating the similar 

 genus Eridophyllum, which on account of its internal wall was compared 

 with Acervularia. De Koninck and Dybowski, however, later defined the 

 genus Diphyphyllum as characterized by the presence of an internal wall 

 with regular tabulae within it and by the feeble development of the septa. 

 The group defined by these characters is identical with Rominger's second 

 modification except that this author describes this group as without internal 

 wall. Other writers on Diphyphyllum contend that the internal wall is 

 never but slightly developed. Freeh 2 states that, on account of the inter- 

 nal walls in Diplophyllum caespitosum, Hall's comparison of that 

 species with Diphyphyllum was erroneous, and that it is much more nearly 

 related to Acervularia. It is also distinctly stated that the septa in Diphy- 

 phyllum are feebly developed, while in Diplophyllum they are quite strong 

 and reach the center. 



'Polyp. Foss. Terr. Paleoz. 1851. p. 446. 

 2 Lethaea Palaeozoica, i : 350. 



