Class BRACHIOPODA 



Order ATREMATA 



Family LINGULIDJE 



Genus LINGULA Bruguiere 



Description. Shell thin, linguiform or tongue-shaped, subequivalvate ; 

 elongate-ovate or subquadrate in outline. Brachial valve slightly shorter 

 than the pedicle and with a slightly thickened hinge-line. The pedicle 

 opening common to the two valves. Surface of the valves usually shining, 

 smooth or marked by concentric or radiating striae. Internally, the 

 muscular impressions are numerous but usually indistinct. 



Remarks. The genotype of Lingula is the recent species L. anatina, but 

 from the state of our knowledge of the characters of the ancient species 

 which have been referred to the genus, there seems to be reason for sepa- 

 rating only a few of them generically from the living forms. It is true 

 that the internal characters, especially the arrangement of the muscular 

 scars, are insufficiently known or wholly unknown in many of the species 

 which have been described from Paleozoic faunas, and it is possible that 

 with future increased knowledge of these characters other generic dif- 

 ferentiations may be drawn. Ordinarily it is difficult or impossible to 

 differentiate between the two valves of a fossil species of Lingula. 



LINGULA MEMBRANACEA "Winchell 

 Plate I, Fig. 5 



1863. Lingula, membranacea Winchell, Proc. Acad. Nat. Sci. Phil., p. 3. 

 1900. Lingula membranacea Weller, Trans. St. Louis Acad. Sci., vol. 10, 

 p. 65, pi. 1, fig. 20. 



Description. Shell ovate-subquadrangular in outline, the greatest width 

 towards the front, the valves very flat. Postero-lateral margins nearly 

 straight as they approach the beak, where they meet in a very broadly 

 obtuse angle, rounding into the lateral margins distally; lateral margins 

 nearly straight or very gently convex, diverging slightly anteriorly ; the 

 antero-lateral margins rounding into the truncated anterior margin. The 

 beak depressed and inconspicuous, not quite reaching the posterior 

 margin. Surface marked only by concentric lines of growth varying 



