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 ridge« di'^erging from the apex, and from these the plate 
rises toward the sides into u^iidedly 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 lamellaB are carried forward, following the curves of the valves 
Fig. 208. Cryptonella planirostra,M&ll- 
The brachidium; showing the long descending and ascending lamellie. 
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. 
