198 PALEONTOLOGY OF NEW YORK. 



On the other hand, the Devonian species, R. sub-Wilsoni, d'Orbigny, possesses a 

 solid, undivided hinge-plate and a highly developed cardinal process, as was 

 shown by Davidson, in 1852, and by (Ehlert, in 1884 ; and though having ex- 

 ternal contour, median septum and unsupported teeth, as in R. Wilsoni, should 

 not be placed in too intimate association with the latter. The generic charac- 

 ters of R. suhwilsoni are positive, those of R. Wilsoni are unsubstantial. If 

 WiLSONiA has any value as a distinctive designation it is subordinate to Cama- 

 ROTCECHiA, and as such may serve to characterize the subcuboidal shells of this 

 group which, like R. Barrandii, Hall, and the species constituting the proposed 

 subgenus Plethokhynchus, have the teeth unsupported by dental lamellae. To 

 adopt the name Wilsonia for all the shells possessing the internal characters of 

 R. Wilsoni, without regard to external form, and thus make it the equivalent of 

 the group Camarokechia, would be to deviate widely from the intent of the 

 authors of the term ; hence, per contra, it becomes necessary to restrict the 

 application of the name to very narrow limits. 



In American faunas the typical Wilsonia is but sparsely represented. With 

 it may be placed the species R. Saffordi, Hall, to which reference has been made. 

 Perhaps the R. ventricosa, Hall, of the Lower Helderberg fauna (Shaly lime- 

 stone), a shell referred to in the discussion of Camarot(echia, should be associ- 

 ated with it. Rhynchomlla Wilsoni is a species of wide distribution in the 

 European Upper Silurian, and has been described in Great Britain, Sweden, 

 Russia and Spain ; Davidson gave its vertical range as from the Llandovery to 

 the Ludlow periods. It is probably true that the very few other species ol 

 similar type of exterior, which have been described from the Wenlock and 

 equivalent faunas, are congeneric, but this statement can be made only with 

 reservation. 



Bayle, in 1878, proposed* to use the term Uncinulina for a species described 

 by him as Uncinulina fallaciosa, from the lower Devonian of Nehou and else- 

 where. To Dr. (Ehlert, again, we owe the elaboration of this shell, f The 

 species is subcuboidal in form, less globose than R. Wilsoni, but with the abrupt 



• Explication Carte gfiolog. France, Atlas, pi. xiii, fig«. 13-16. 

 t Op. cU., p. 420, pi. xviii, figs. 5a-o. 1884. 



