MANUAL OF THE MOLLUSCA. 
Rensseleéria, if not synonymous with, is closely related to, 
Meganteris. 
Fossil, 11 species. Silurian to Devonian. Europe, North 
America. 
CENTRONELLA, Billings, 1859. 
Etymology, diminutive of kentron, a spur. 
Type, Rhynchonella glans-fagea, Hall. 
Shell haying the general form of Terebratula. Dorsal valve 
with a loop consisting of two riband-like lamelle, 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, approaching in some respects to 
Waldheimia. ‘ 
Distribution, 4 species. Devonian. North America. 
LeprooaiiA, Hall, 1859. (Ccelospira, Hall). 
Appears to differ from Centronella only in consisting of. 
species which have the surface ribbed instead of smooth. 
Distribution, 9 species. Mid. Silurian—Devonian. Europe, 
North America. No true Terebratule have been found in 
beds older than the Devonian. 
FAMILY IJ.—SPIRIFERIDA.* 
SYRINGOTHYRIS, Winchell, 1863. 
Fig. 19. Section through the beak of the ventral valve of S. typa (Winchell). 
1, dental plates or lamells ; ¢, tube incomplete ; 7, mesial ridge. 
Examples, 8. typa, Winchell, Fig. 19; Spirifera distans, Sow. 
Shell like that of Spirifera, with an elongated hinge-line. 
Ventral valve with a broad mesial sinus, a very broad area, and 
a narrow triangular fissure closed towards the apex by an 
external conyex pseudo-deltidium ; beneath which, and diverg- 
ing from it, 1s another transverse plate connecting the vertical 
dental lamellz, which are incurved so as to nearly join their 
inferior edges, thus forming a fissured tube, which projects 
beyond the limits of the plate frem which it originates into the 
interior of the shell. A low median ridge extends from the 
See p. 271. : 
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