252 



Die Sihirische Fa una dcs Wcstlichen Ttfinessee. 



irregularly dispersed, the spaces between being filled with a compact 

 coral mass ; .the flat lower surface, on the other hand, displaying only 

 concentric wrinkles. At first sight this species would seem to resem- 

 ble the Cha'tetes Petropolitanus, but further investigation shows that 

 the cellular openings are not polygonal and do not touch each other, as 

 in the latter, but are circular and separated by intermediate spaces, whose 

 diameter is once again and sometimes twice as great as that of the open- 

 ing themselves. The manner of the distribution of the cellular open- 

 ings is something like that of the HelioUfes, but whilst there the spaces 

 between the openings are porous, in this case, at least upon the upper 

 surface, the spacer are perfectly compact, without pores and holes. A 

 Ijorder, generally somewhat raised fi'om the surface and plainly visi- 

 ]}le, surrounds each opening. 



All these characteristics conform entirely to the genus of Edwards 

 and Haime. Yet I am by no means certain of the identity of the 

 American fossil with that described by the French author ; on the 

 contrary, I have some hesitation in placing them in the same category. 

 For, in the first place, the inner structuie of the specimens before me 

 could not be ascertained, and then the cellular openings have compar- 

 atively a notably smaller diameter than that of the other species of 

 Theocostegites. In the smaller specimens the openings are of a needle 

 form, and hardly visible to the naked eye as distinct points. When the 

 upper surface is disintegrated, the cup-shaped openings are much wider, 

 and the i-esemblance with the Calamopora or Chcetetes is more apparent. 

 But then the cups are separated by much denser pai'titions than in the 

 latter genus. 



Orthis jisslplica — (Rcemer. ) 



Shell depressed, convex, transverse, oval, long cardinal line not, 

 liowever, equal in length to the greatest breadth of the shell. Sur- 

 face covered with numerous (40 in the whole contour), radiating 

 curved plications, which increase in number, either through bifurca- 

 tion, or by intercalation, similar to bifurcation. The new plications 

 are much less distinct than the chief folds, in as much as they run into 

 the latter and become merged with it. The spaces between the 

 radiating folds are marked by sharply projecting transverse lines. 

 The perforated valve (ventral valve, Davidson,) is moderately convex, 

 and provided with a distinct, moderately elevated umbone. The other 

 va ve is flat, with its middle part slightly depressed. 



The general appearance of this species corresponds so nearly witli 

 many other species of this genus, that at first sight it would appear tc* 

 be a well known form. When, however, we undertake to define it, 



