BRACHIOPODA. 79 



Mr. Billings proposed this term for species of meristelloids in which the 

 hinge-plate is so greatly modified as to be apparently absent. Upon examina- 

 tion of specimens of his typical species, Atnjpa scitula, Hall (which is also 

 probably identical with his second species, Charionella Circe), this structure is 

 found to be of the following character : The general appearance is that of a 

 pedicle-valve ; two ridges, strongly recurved at their edges, pass along the mar- 

 gins of the delthyrium, enclosing the dental sockets ; they are supported by 

 thin lamellae which converge toward the bottom of the valve ; the crura arising 

 from the extremities of the lateral ridges, are short and curved outward ; the 

 central portion of the plate must be considered as absent, or as very concave 

 and merged in the substance of the valve. 



This is a wide departure from the structure of the hinge-plate in the other 

 spire-bearing brachiopoda. In other respects, however, except the almost total 

 obsolescence of the median septum of the brachial valve, Charionella scitula is 

 a near ally of Meristella. Tlie muscular scars in the pedicle-valve are 

 essentially similar, though in the brachial valve they are considerably more 

 pronounced than in Meristella, occupying an elongate-oval space and being 

 divisible into an anterior and posterior pair. Our preparations indicate that 

 the loop has the same structure as in Meristella. 



Assuming the identity of Atrypa scitula. Hall, with Charionella Circe, Billings, 

 there is no other species known to us which can safely be referred to this genus. 

 Mr. Billings subsequently* applied this generic term to his Charionella ? Hyale, 

 from the Guelph limestone, and to tlie Meristella rostrata, Hall, of the Hamilton 

 group (Tully limestone) ; specimens of the former from Elora, Ontario, indi- 

 cate that the species is a Whitfieldella. Of the latter we have seen no speci- 

 mens showing the structure of the hinge. 



* See PalKozoic Fossils, vol. i, p. 166, fig. 150. 1862. 



