UINTACEINUS: ITS STEUCTUEE AND EELATIONS. 



87 



decidedly with the size of the specimens. The following averages, taken 

 from the general table, show this very clearly: — 



EECAPTTULATION AS TO INTEESECUNDIBEACHS AND 

 INTEEPINNULAES. 





Number of Plates in illBr Areas. 



Interpinnulars. 



Width of Calyx. 



lor 2. 



3 or 4. 



5 or more. 





Per ceot. 



Number. 



Number. 



Number. 



Per cent. 



Number. 



Per cent. 



Less than 25 mm. 

 25 to 49 " 

 50 to 60 '' 

 61 to 75 " 



62 

 32 



28 

 15 



32 

 63 

 64 

 15 



19 



90 



126 



49 



1 



16 



32 



28 



2 



9 



14 



30 







8 



14 



19 







4 



6 



20 



What, then, have we left to distinguish the European from the 

 American species ? Schlueter's specimen of U. westf aliens, and I judge also 

 Bather's, from his account of its discovery, is more plump and rotund than 

 U. socialis as hitherto found. This might be due to a greater thickness of 

 the plates, but this is not probable. It would seem probable that the 

 specimens of U. westf aliens thus far discovered were isolated, — in the sense 

 that they were free from attachment to others, — and were preserved in 

 their rotund form by some exceptionally favorable condition of fossilization, 

 as the specimens of Marsupites are frequently found. Even the swelling of 

 the interradii we have occasionally in the American specimens. If U. tvesU 

 falicus is a good species, then it exists in America, along with U. socialis, 

 and in the same colony ; for, as already stated, and as clearly appears 

 by the foregoing table, there are specimens which, in the essentials 

 relied upon to separate the species, are not distinguishable from it. 

 But these specimens, considering their mode of occurrence, and the 

 great variation exhibited in the supposed distinctive characters, cannot 

 be separated from U. socialis. From all these facts it follows irresistibly, 

 in my opinion, that U. westfaliciis cannot be distinguished from U. socialis^ 

 and that the two represent but one species, which of course must take the 

 older name, U. socialis. 



The fact that they come from different continents is of itself no proof 

 that these are distinct species. There is no a priori reason why a species 

 found in America should not occur in Europe also. It has been the custom 



