BRACHIOPODA. 57 



while in Lingulella the opening for the passage of the pedicle is a sharply de- 

 fined slit, not merely making a depression upon the sur- 

 face of the cardinal area, but apparently penetrating it 

 from apex to cardinal line Varying conditions of pres- 

 ervation will often make the detei'mination of this feature 

 difficult ; but, aside from the character of the cardinal 

 area, there is little known ot the type-species ot Lingu- M^u^m, alter Davidson. 

 LELLA which can be satisfactorily regarded as of generic value.* Mr. Salter 

 suggested a similarity in the muscular scars of L. Davisi, and those of Obolus 

 and Obolella ; Davidson, however, was unable to find examples of the species 

 showing these impressions satisfactorily,! but called attention to the coarse 

 punctse over the visceral surface of one individual. 



The generic term Lingulella lias been used with considerable freedom b}' 

 both American and English writers, but while there must remain a degree of 

 uncertainty in regard to the correct generic character of many species now in- 

 cluded under this name, there are a few primordial forms which are pretty well 

 understood, both externally and internally ; but whatever conclusions in regard 

 to the generic features of Lingulella are derived from the study of these, 

 must be dependent upon the results of future investigations upon the type- 

 species, L. Davisi. 



Mr. C. D. Walcott has given^ figures of Lingulella Ella, Hall and Whitfield, 

 which show not only the characteristic cardinal area and pedicle-slit, but 

 give very distinctly the character of the muscular impressions on both valves. 

 There will also be found on Plate I, figs. 1-4, of this volume, illustrations of 

 the interior of both valves of Lingulella calata, Hall (Orbicula, Hall, 1847, 



* Di'. King was strongly disiucliueJ to iijuiit the term Linoulella. In his work upon the " Chai-acters 

 oi Lingula anatina," he says: "The deltidium is a variable sti'uctiire in Palliobranchs generally ; and 

 its modifications are far from being understood. As regards the deltidium in the genus under consideration 

 [Lingula], one circumstance is I'emarkable : it has been in a gi-eat measure overlooked ; at least I can find 

 little, or rather no notice of it in the writings of previous observers. It is this oversight which led the late 

 J. W. Salter to institute his genus Lingulella, which he typified with the Cambrian Lingula Davisi, under 

 the belief that its 'pedicle-groove' and ' hinge-area' do not characterize any species of the old Brugiiicrian 

 genus" (Ann. and Mag. Nat. Hist., Fourth Ser., vol. xii, p. 14. 1S73). 



t Silui'ian Brach., p. 55. 



I United States Geological Survey, Bull. 30, pi. vii, tig. 2 ; and pi. viii, tigs. 4 a, b, c. 1886. 



