BRACHIOPODA. 57 



while in Ltngulella the opeuins for the passage of the pedicle is a sharply de- 

 fined slit, not merely making a de^wession 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 determination of tiiis feature ,^ 

 difficult ; but, aside from the character of the cardinal / 

 area, there is little known of the type-species of LiNi;u- ''',^M%„SSXw;'ioi;f"" 

 LELLA which can l)e satisfactorily regarded as of generic value.* Mr. Salter 

 suggested a similarity in the muscular scars of L. Bavisi, ami those of Obolus 

 and Obolella ; Davidson, however, was unable to find e.xamples of the species 

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

 puncta3 over the visceral surface of one individual. 



The generic term Lingulella has been used with considerable freedom by 

 both American and English writers, but while there nuist 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 giveni figures of Linguklla 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 Linguklla calata. Hall (Orbicula, Hall, 1847, 



•* Dr. King was strougly disinclined lo admit ilie term Li>(itLiiLL.\. In his work mioii llie •• Characlui'S 

 of Lingula aiMtirm," he says: "The deltidium is a vai-iable structure iti Palliobr.inchs generally ; and 

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

 [LiSGCLAJ, one circumstance is remarkable: it has been in a great measure overlooked ; at least 1 can find 

 little, or rather no notice of it in the wiitings of previous observers. It is this ovei-sight which led the late 

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

 the belief that its 'pedicle-gr-oove' and ' hinge-area ' do not charactei'ize any species of the old BruguiJrian 

 genus" (Ann. and Mag. Nat. Hist., Fourth Ser., vol. xii, p. 14. 1873). 



t Silurian Brach., p. 55. 



J United States Geological Survey. Bull. 30, j.l. vii, fig. 2 ; .in.l pi. viii, figs. 4 a, b, c. 1886. 



