280 MISSISSIPPIAN BRACHIOPODA 



the crura become free a narrow transverse band joins their bases. The 

 characters of the brachidium not completely determined, but it is clearly 

 of the short, Dielasma-like type. Shell structure finely punctate. 



Remarks. In the arrangement of the internal features of the apical 

 portion of the brachial valve this genuS is perhaps more closely allied to 

 Crancena than to any other of the generic types here recognized. It differs 

 from Crancena, chiefly in the reduction of the hinge-plate to a narrow trans- 

 verse band joining the crural bases, while in Crancena it is elongate with a 

 comparatively small apical perforation and with the crura originating as 

 a pair of ribs diverging anteriorly from near the apex. The difference in 

 shape, viz: the much compressed shell and the erect beak of the pedicle 

 valve are other features which easily separate the members of this genus 

 from all the recognized species of Crancena. 



DlELASMELLA COMPRESSA Weller 



} 



Plate XXX, Figs. 43-55 



1906. Eunella compressa Weller, Trans. St. Louis Acad. Sci., vol. 16, 



p. 442, pi. 6, figs. 13-16. 

 1911. Dielasmella compressa Weller, Jour. Geol., vol. 19, p. 447, figs. 7a-f. 



Description. Shell very small, lenticular, compressed, subovate in out- 

 line, usually longer than wide but sometimes a little wider than long, the 

 greatest width near the mid-length of the shell. The dimensions of two 

 complete specimens are : length of pedicle valve 5.9 mm. and 6 mm., length 

 of brachial valve 5.1 and 5.5 mm., width 5 mm. and 6.5 mm., thickness 2 

 mm and 2.5 mm. 



Pedicle valve depressed convex, the greatest convexity posterior to the 

 middle, the surface usually very gently convex towards the lateral mar- 

 gins but sometimes a little compressed antero-laterally, near the postero- 

 lateral margins the surface is abruptly inflected to the cardinal extremi- 

 ties ; the median portion of the valve differentiated from the lateral slopes 

 as a narrow, somewhat ill-defined, flattened region which is sometimes 

 slightly depressed medially in a faint sinus ; the beak pointed, nearly 

 erect, pierced by a subcircular foramen which only partially encroaches 

 upon the umbonal portion of the valve ; delthyrium closed by a pseudo- 

 deltidium except in its apical portion which is a part of the foramen. 

 Internally the dental lamella? are well developed and are of moderate 

 length. 



Brachial valve equally or a little more convex than the pedicle, the 

 greatest convexity posterior to the middle, the surface with a nearly 

 straight slope along the median line from the middle of the valve to the 

 front, convexly curved to the beak, the lateral slopes very gently convex 

 and sometimes a little compressed towards the cardinal extremities; the 

 median portion of the valve differentiated as a rather narrow, flattened 



