252 MISSISSIPPIAN BRACHIOPODA 



the median portion of the valve undifferentiated from the general convex- 

 ity of the valve or rather indefinitely flattened towards the front, never 

 depressed in a mesial sinus or elevated in a fold; beak prominent and 

 incurved beneath that of the opposite valve. Internally the socket plates 

 are joined transversely by an elongate, concave hinge-plate which is per- 

 forated at the apex, anteriorly the socket plates are reduced and the lat- 



M I J 



FIG. 26. A series of ten cross-sections of the rostral portion of the shell of 

 Crancena sulcata (X 2%), showing the hinge-plate perforated posteriorly, and 

 the crural ridges. 



era! attachments of the hinge-plate to the inner surface of the valve re- 

 treat from the lateral margins, a pair of ridges diverge anteriorly from 

 near the apex upon the concave surface of the hinge-plate, which become 

 the bases of the crura, the concave hinge-plate continues to join the crural 

 bases after their lateral connection with the inner surface of the valve has 

 become discontinued; complete brachidium not known, but it is believed 

 to be short and Dielasma-like in form. 



Remarks. This species has commonly been identified with the form here 

 defined as Girtyella turgida, but it is a larger species besides being totally 

 different from that one in the apical portion of the interior of the brachial 

 valve ; it differs externally from that species in the absence of a mesial 

 sinus in the brachial valve and in having the beak of the pedicle valve a 

 little less incurved. The species resembles Dielasma sinuata externally, but 

 it is much smaller and the different mode of attachment of the crural 

 plates in the apex of the brachial valve is a character of generic value. 



Horizon. Salem limestone. 



CRAN^ENA ( ?) ALLEI (Winchell) 

 Plate XXXIV, Fig. 51 



1865. Centronella Allei Winchell, Proc. Acad. Nat. Sci. Phil., p. 123. 

 1901. Dielasma allei Weller, Trans. St. Louis Acad. Sci., vol. 11, pp. 162 

 and 189, pi. 14, fig. 10. 



Description. Shell small, subovate or ovate-subpentagonal in outline, 

 the anterior margin rounded, the greatest width near the mid-length. 

 The dimensions of a pedicle valve are: length 10.5 mm., width 9 mm., 

 convexity 2.5 mm. The dimensions of a brachial valve are: length 9 

 mm., width 8.8 mm., convexity 2 mm. 



Pedicle valve with its greatest convexity posterior to the jniddle, the 

 surface moderately convex in the umbonal region and rather abruptly 



