BRACHIOPODA. l'J7 



and by many European authors has been applied to shells of this character. 

 Mr. Davidson did not adopt it; Drs. Waagen and (Ehlekt* have objected to its 

 admission on account of its morganatic introduction and have preferred to use 

 the term Uncinulus, proposed by Bayle in 1878. 



A critical study of this group of subcuboidal shells has compelled the adoption 

 of somewhat different conclusions than those expressed by other investigators in 

 regard to their generic values and appropriate designation. Thus far the broader 

 application of the term Wilsonia (a name which should be accredited to Kayser 

 rather than to Quenstedt, the former being not only the first to use the term, 

 but accompanying it with a careful account of the characters of the group), has 

 rested mainly upon external features. Davidson did, indeed, as early as 1852, 

 describe the muscular scars and interior apophyses both of R. W/lsoni, Sowerby, 

 and also of i?. sub-Wilsoni, D'Orbigny, the latter a lower Devonian shell from Nor- 

 mandy (Nc'hou), and the type of Bayle's genus Uncinulus ;t and to CEhlert j; we 

 owe a most careful delineation of the internal characters of the latter. Both 

 of these species are characterized by the great size and depth of the diductor 

 scars of the pedicle-valve, the thickened teeth unsupported by vertical lamellae, 

 and both have a well developed median septum in the brachial valve. But 

 they differ most conspicuously, and most importantly, in the structure of the 

 hinge-plate. In R. Wilsoni (Wilsonia) the plate is very small, is divided medi- 

 ally by a shallow incision into distinct crural bases, and has no cardinal process. 

 In fiict the structure is not unlike that of Camauotcechia, though never so highly 

 developed as in the Devonian species of that genus. So far as we are aware, 

 among the many figures of R. Wilsoni to be found in literature, none have been 

 given which show the construction of this part; those upon Plate LVIII have 

 been made from a clean internal cast of the American shell identified by 

 DE Verneuil with R. Wilsoni, but subsequently termed R. Saffordi, Hall, and 

 which occurs in the Niagara fauna of Perry county, Tennessee, at Louisville, 

 Kentucky, and in the upper members of the Arisaig series, in Nova Scotia. 



* Dr. CEiiLERT, in some of his later papers, has withdrawn his objections and adopts Wilsonia (Quen- 

 stedt), Kayser, in preference to llNCrNrLus, Bayle. 

 t Explication de la carte geolog'. France. 1S78. 

 X Bull. Societe geolog France, 3d ser., vol. xii, pi. xxi, fig's. 1, a-s. 1884. 



