BRACHIOPODA. 131 



obliquely outward, toward the lateral slopes of the pedicle-valve, similar to 

 those of Atrypa, though more divergent. 



In 1882, Mr. Davidson introduced* the term Bifida as a generic designation 

 for the species above referred to by Schnur as a very close ally of Terebratula 

 venusta, viz.: T. lepida, Goldfuss, as quoted by d'Archiac and de Verneuil,! 

 the Atrypa lepida, Davidson,^ and the Retzia lepida, Kayser, § a form occurring 

 in association with T. venusta in the Devonian of the Eifel, and known also 

 in the middle Devonian of Torquay. 



Mr. Davidson has shown, from preparations made by the Rev. Mr. Glass, 

 tliat the spiral coil is loosely arranged, the ribbon making but four or five 

 volutions ; the apices of the cones are directed obliquely outward toward 

 the lateral slopes of the pedicle-valve. The loop 

 is described as simple, "like that in Meristina 

 [ Whitfieldella], with the exception that it is 

 placed nearer to the attachments of the hinge- 

 plate, and that, at the point where the two lamellae 

 composing the loop join, there is a short bifur- 

 cation directed upwards" (p. 28). It was this 

 alleged bifurcation of the loop that suggested the fig. m. 



T, T , 1 1 • r- ,1 • 1 ii i Bifida lepida, Goklluas. 



name Bifida, and on the basis of this also that ^,^^ b,acuiaium as represented by 

 Mr. Davidson compared and classified the shell Davidson ivom preparations by glass. 



with the genus Whitfieldia (^Meristina.) The accompanying figure shows 

 the structure of this organ as described by him. A careful study of this 

 shell II has led to a quite diflferent result in regard to the structure of the 

 loop. These observations have been made not only from translucent prepara- 

 tions, but also by consecutive sectioning of opaque specimens, and the 

 conclusions verified by frequent repetition of the process. 



The accompanying figures are of sections made from opaque specimens 

 cut in a plane vertical to the longitudinal axis of the shell, the series 



* Supplement to British Devonian Brachiopoda, p. 21. 



t Transactions of the Geological Society of London, second sei'., vol. vi, p. 386. 1840. 



I British Devonian Brachiopoda, p. 52. 1864. 



§ Zeitschr. der deutschen geolog. GesellschafI, vol. xxiii, p. 559. 187). 



I From specimens from Gerolsteiu in the Eifel, furnished by Dr. E. Holzapfel, of Aachen. 



