302 MISSISSIPPIAN BRACHIOPODA 



Brachial valve less convex than the pedicle, the greatest convexity 

 near the middle, compressed towards the cardinal extremities ; the mesial 

 fold rounded, but little elevated above the general surface of the valve; 

 cardinal area very narrow, lying in nearly the plane of the valve ; plica- 

 tions similar to those of the opposite valve and alternate with them. In- 

 ternal characters not observed. 



Besides the plications the surface of each valve is ornamented by con- 

 spicuous, somewhat irregular, lamellose, imbricating, concentric markings, 

 about two or three occupying the space of one millimeter. 



Remarks. In none of the specimens of this species, which have been 

 examined by the writer, has the punctate shell structure of the genus Spiri- 

 ferina been observed. In the original description of the species, however, 

 it is stated "internal surface of the valve marked with numerous indented 

 punctations, " and this would seem to indicate that the species possesses 

 this characteristic structure of the genus Spiriferina. Not infrequently 

 in undoubted species of Spiriferina, this structure is obscure and cannot be 

 detected upon many examples, but an examination of a sufficient number of 

 specimens usually leads to its recognition. This species differs from most of 

 the other members of the genus here described, also from members of the 

 genus Spiriferina, in its stronger and coarser concentric lamellge. The 

 number of plications is a somewhat variable character, but they are al- 

 ways coarser and less numerous than usual in the genus. The species 

 which most closely resembles this one is D. missouriensis, and the differences 

 between the two forms will be considered under the discussion of that 

 species. 



Horizon. Louisiana limestone. 



DELTHYRIS MISSOURIENSIS "Weller 

 Plate XXXVI, Figs. 9-14 



1906. Delthyris missciiriensis Weller, Trans. St. Louis Acad. Sci., vol. 16, 

 p. 445, pi. 6, figs. 23-26. 



Description. Shell smiall, wider than long, the greatest width usually a 

 little in front of the hinge-line, and the cardinal extremities narrowly 

 rounded. The dimensions of a pedicle valve are: length from umbo to 

 front margin 10 mm., width 12.5 mm., length of hinge-line 11 mm., convex- 

 ity 4.5 mm., height of cardinal area 2.2 mm. The dimensions of a large 

 brachial valve are : length 9 mm., width 13.4 mm., convexity 3 mm. 



Pedicle valve rather strongly convex, the convexity extending out to 

 the cardinal extremities, the umbo prominent, the surface curving rather 

 abruptly to the anterior margin and sloping in nearly straight lines to 

 the cardinal extremities ; mesial sinus originating at the beak, of moderate 

 width, rather shallow, and rounded or somewhat flattened in the bottom ; 

 the beak rather obtuse, a little incurved; cardinal area of moderate 



