310 TEREBBATULIDJE. 



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. rectiroatra^ Hall. 



MEGANTERis, Suess, 1856. 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 Y-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 essentiallj^ 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 haemal valve. Sil. ; N. Am. 

 Dev. ; Eur. W. Archiaci, Suess. 



Centronella, Billings, 1859. 



Etym. — Diminutive of kentron, a spur. 



Syn. — Cryptonella, Hall (part). 



JDistr. — 4 sp. Devonian ; North America, C. glans-fagea, 

 Hall (cxxxv, 25, 26). 



Shell having the general form of Terebratula. Dorsal valve 

 with a loop consisting of two riband-like lamellae, 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. 



LEPTOccELiA, 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 Terebratulge have been found in beds 

 older than the Devonian. L. imbricata^ Hall. 



? HiNNiPHORiA, Suess, 1858. H. globularis, Suess. Jurassic; 

 Stramberg. 



Renssel^ria, Hall, 1859. 



Etym. — Dedicated to the late Hon. Stephen Van Rensselaer. 



Syn. — Atrypa, Conr., 1839. Pentamerus, Yanuxem, 1843. 



Distr. — Fossil, 11 sp. Silurian — Devonian; Europe, N.Am. 

 E. ovoides, Hall (cxxxv, 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 

 dental sockets between the shell and a strong process from which 



