144 TABULATE CORALS. 



sometimes uniting with one another, but not subvesicular in 

 character. The " vermiform body " of Pleurodictyum pro- 

 blematicum, Goldf., is sometimes (always ?) present in the 

 interior of the corallum. 



Obs. This pretty little species seems to have been first 

 named Astrcea stylophora by Eaton, I presume in his ' Geolo- 

 gical Text- Book ' (published in 1832); though I am unable to 

 consult this work, and cannot speak positively upon this point. 

 Dr Rominger (loc. cit.\ in describing his Michelinia trochiscus, 

 gives the above as its synonym ; and assuming the correctness 

 of this, it would seem that Eaton's specific name has the clear 

 right to be retained, as no other species of Michelinia or Pleuro- 

 dictyum has been similarly entitled. Should it be found neces- 

 sary, for any reason, to abandon Eaton's name, then it would 

 be a question whether the present species should not stand as 

 Pleurodictyum Americanum, under which name it was well 

 figured and briefly described by Professor Ferd. Roemer in 

 1876 (Leth. Pal., PL XXIII., figs. 2 a, 2 6). Through the kind- 

 ness of my friend Mr George Jennings Hinde, I possess a few 

 specimens of this remarkable form, which is of special interest 

 as presenting us with the actual corallum of a form unques- 

 tionably congeneric with Pleurodictyum problematicum, Goldf, 

 though apparently specifically distinct. These I have sub- 

 mitted to a careful examination by means of thin sections, 

 and I shall now give the principal results of this, along with 

 some remarks upon the genus Pleurodictyum, and upon P. 

 problematicum, Goldf. 



As before remarked, P. problematiciim is only known by 

 casts in sandstone, which are of not very rare occurrence in the 

 Devonian deposits of Europe and of Devonshire. Precisely 

 similar casts though probably specifically distinct occur in 

 the Onondaga sandstones of North America, and have been 

 well described and figured by Meek and Worthen, with a 

 somewhat doubtful reference of them to the European species 

 (Geol. of Illinois, vol. iii. p. 405, PI. IX., figs, i a-\ c, 1868). 

 In both these cases the fossil (fig. 22, A and B) consists of a 



