BRACHIOPODA. 287 



primary importance we must accept this rehabilitation of the genus. Thus 

 constituted Cryptonella includes a group of terebratuloid shells having the 

 following characters : 



Valves subequally convex ; elongate-oval in outline, broadest in the pallial 

 region. Pedicle- valve with prominent, erect or slightly incurved umbo ; del- 

 tidial plates well developed ; foramen circular, apical, rarely encroaching upon 

 the umbo, or becoming oval as in many species of Dielasma ; the inverted 

 pedicle-sheath or collar is slightly developed within the aperture. The teeth 

 are strong and supported by dental lamellae which divide the umbonal cavity 

 into three chambers ; near the apex they join the somewhat thickened scar of 

 the pedicle-muscle, and extend beyond its anterior margin with a slight con- 

 vergence, resting always on the bottom of the valve. The pedicle-muscle 

 makes the strongest scar of all the muscular bands, the adductors being narrow 

 and central, and the diductors scarcely delimited. 



In the brachial valve the hinge-plate is large, elongate and concave ; it is 

 divided by two low ridges diverging from the apex, and from these the plate 

 rises toward the sides into decidedly elevated socket-walls ; between the diverg- 

 ing ridges the surface is rather deeply depressed, and, toward the apex, is per- 

 forated by a circular foramen. The crura are slender, very short, curving 

 inward and upward, making two long and narrow crural apophyses. The 

 descending lamellae are carried forward, following the curves of the valves 



Kio. 20S. Cryptonella planirottra, HaW. 

 The brachidlam; showing the long descending and ascending lamellae. 



for nearly two-thirds the length of the shell, and abruptly reflected; the 

 ascending lamellae returning to within a short distance of the crural apophyses. 



