310 TEREBRATULID. 
flatter, with a deep marginal sinus, folded in the middle; loop 
very long, fringed, the blades widened near the connecting bridge; 
septum strong. Jurassic, Cretaceous. W. bivallata, Deslong. 
CRYPTONELLA, Hall, 1867. Loop exactly resembling that of 
Waldheimia proper, except in the addition of a transverse band 
from one side of the apophyses to the other behind the crura. 
Devonian. W. rectirostra, Hall. 
MEGANTERIS, Suess, 185(6. Shell orbiculate, somewhat com- 
pressed, nearly equivalve; area of neural valve small, apex 
inconspicuous, minutely foraminated, punctate; deltidia small, 
wide, united ; cardinal process prominent, with a V-shaped pro- 
cess near the apex for the insertion of the cardinal muscles, 
sulcated on each side. with the base excavated ; cardinal border 
broad, wide, rugose ; loop essentially as in Waldheimia, but with 
very long crura, the main stems of the apophyses being given 
off at a sharp angle with the crura, reflected abruptly and the 
posterior part of the reflected loop behind and below the crura; 
there is a faint mesial septum in the hemal valve. Sil.; N. Am. 
Dev.; Eur. W. Archiaci, Suess. 
CENTRONELLA, Billings, 1859. 
Ltym.—Diminutive of kentron, a spur. 
Syn.—Cryptonella, Hall (part). 
Distr.—4 sp. Devonian; North America. (C. glans-fagea, 
Hall (exxxv, 25, 26). 
Shell having the general form of Terebratula. Dorsal valve 
with a loop consisting of two riband-like lamella, which were 
united at an acute angle at the point of greatest extension, 
whence they recurve in a thin vertical plate which is not attached 
at either margin. 
LEPTOCa@LIA, Hall, 1859. Appears to differ from Centronella 
only in consisting of species which have the surface ribbed 
instead of smooth. 9 sp. Mid. Silurian—Devonian ; Europe, 
North America. No true Terebratule have been found in beds 
older than the Devonian. ZL. imbricata, Hall. 
? HINNIPHORIA, Suess, 1858. H. globularis, Suess. Jurassic ; 
Stramberg. 
RenNsseLa£R1A, Hall, 1859. 
Liym.—Dedicated to the late Hon. Stephen Van Rensselaer. 
Syn.—Atrypa, Conr., 1839. Pentamerus, Vanuxem, 1843. 
Distr.—Fossil, 11 sp. Silurian—Devonian; Europe, N. Am. 
RR. ovoides, Hall (exxxv, 27). 
Shell ovoid or suborbicular, without mesial fold or sinus; beak 
prominent, acute, more or less incurved; foramen terminal, 
sometimes concealed. Ventral valve with two diverging cardinal 
teeth supported by strong dental plates. Dorsal valve with the 
5 . 
dental sockets between the shell and astrong process from which 
