280 NEW YORK STATE MUSEUM 



has supplemented these by a profusion of figures of other Siluric shells hav- 

 ing similar character. It has been usage to refer the Upper Devonic shells of 

 like aspect to this Siluric genus. Chenu J and Zittel, 2 cite C. cornucopiae 

 Goldfs., a German Clymeniakalk species, as typical of the genus and use 

 this for purposes of illustration. 3 Various authors have incidentally referred 

 such Devonic shells as we have here to consider to the genus Cardiola, but 

 no one has studied them as carefully as Beushausen, who, cautiously and 

 with reserve, also employs this term as the present most convenient recepta- 

 cle for them. This procedure can not long be justified. Granting the 

 general similarity in aspect of these shells with Cardiola interrupt a, 

 we find structural differences in the early and later forms which seem to us 

 reliable, and these we should supplement by the following general consid- 

 erations : (i) an a priori consideration, that these late Devonic shells, 

 connected with the .Siluric Cardiolas by very few representatives, are 

 improbably of the same generic character ; (2) the evidence that the 

 influences (whether external or internal) which have effected the paleo- 

 conch condition in so many of these lamellibranch genera, expressed in 

 tenuity of shell, loss of special articular development and shown in all 

 the genera which are properly distinctive of this fauna, have similarly 

 affected this group of Cardiolas, and endowed them with an expression 

 which entitles them to distinction ; (3) the unavoidable conclusion that 

 these shells are opisthogyre in the same sense as are Lunulicardium, 

 Honeoyea and Paraptyx, while there is at present no ground for assum- 

 ing that the typical Siluric Cardiola is of this character. 



In respect to structure we observe (1) the extreme tenuity of the 

 Devonic shells, (2) the general prevalence of an extremely fine, delicate, 

 radial striation contradistinguished from the coarse ribbing of C. inter- 

 rupta and its Siluric allies, (3) a diminution to or almost to extinction of 

 the cardinal or ligamental area beneath the beak, (4) the presence of radial 



1 Manuel de conchyliologie. 



2 Grundzuge d. Paleontologie, etc. 



3 This species was regarded by Sowerby as synonymous with C. interrupta. 



