272 MISSISSIPPIAN BRACHIOPODA 



sockets retreat from the margins of the valve anteriorly beyond the 

 point of articulation and become the bases of the crura which are still 

 joined by the concave hinge-plate and are also supported by lamella; 

 resting against the inner surface of the lateral slopes of the valve. The 

 brachidium short, its free portion apparently being like that of Diclasma 

 and not reaching to the middle of the shell. 



Remarks. Members of this genus have commonly been included in the 

 enus Dielasma, but they differ fundamentally from that genus in the 

 presence of a median septum supporting the hinge-plate of the brachial 

 valve, and in the origin of the bases of the crura from the socket plates. 

 In his description of the species which is selected as the genotype, Girty 

 referred the form to the genus Haritina on account of the presence of a 

 median septum in the pedicle valve, but the brachidium of Harttina is 

 elongate, like that of Cryptonella, reaching nearly to the front of the shell, 

 while that of Girtyella. is short like the brachidium of Dielasma. 



GlRT YELL A CEDARENSIS n. sp. 



Plate XXXTV, Figs. 48-50 



Description. Shell below medium size, subovate in outline, the greatest 

 width anterior to the middle, the anterior margin subtruncate. The 

 dimensions of a nearly complete internal cast are: length of pedicle 

 valve 18.5 mm., length of brachial valve 16 mm., greatest width 15.2 

 mm., thickness 11.9 mm. 



Pedicle valve most convex posterior to the middle, the surface curving 

 abruptly to the postero-lateral margins and becoming somewhat inflected 

 to the cardinal extremities, curving less abruptly to the antero-lateral and 

 anterior margins; mesial sinus shallow, rounded in the bottom, rather 

 broad and ill-defined laterally, originating near the middle of the valve; 

 beak rather prominent and incurved, character of the foramen not shown 

 in the type specimen. Internally the dental plates are rather strong and 

 extend anteriorly from the beak between one-fifth and one-fourth the 

 length of the valve, with only a small amount of divergence. 



Brachial valve about equally convex with the pedicle, the greatest 

 convexity near the middle, the surface curving a little more abruptly to 

 the anterior and antero-lateral margins than posteriorly; mesial fold 

 obsolete, but with the mesial portion of the valve obscurely flattened 

 anterior to the middle of the valve ; the beak pointed and incurved beneath 

 that of the opposite valve. Internally a strong median septum extends 

 anteriorly from the beak for about two-fifths the length of the valve ; the 

 characters of the hinge-plate not fully observed, but so far as determined 

 agreeing entirely with other species of Girtyella. 



Surface of both valves marked by concentric lines of growth which 

 become stronger and more crowded towards the margin. 



