THE DEVONIAN FOSSILS OF CANADA WEST. 147 
Genus Rerz1a.—(King.) 
Reraia.—King. Monograph of the Permian Fossils of England, 
p. 137. 1850. 
Rerzia.—Woodward. Manual of the Mollusca, p. 224. 
Generic characters.—The species of this genus are in general 
smaller than those of Athyris or Spirigera. The form is ovate or 
sub-globular; the ventral valve the largest, with an elevated beak, 
which is perforated at the tip by a small circular aperture; a small 
flat area beneath the beak. In some species there is a shallow mesial 
fold and sinus, or more usually two or three of the ribs in the middle 
smaller than the others. The surface is covered with radiating ribs, 
as in Rhynconella. The internal characters are not yet well known, 
but it is certain that the spiral appendages have their apices turned 
outwards, as in Spirigera. The shell structure is punctate. 
Retzia differs from Spirigera in being strongly ribbed, smaller, the 
beak of the central valve erect, or nearly so, and in haying a small 
flat area beneath the rostral aperture. 
_ Rhynchospira,—Hall, does not appear to me to differ from Retzia. 
The genus is said to range from the Silurian up to the Permian. 
Dedicated (by King) to the celebrated naturalist Retzius. 
Retrzia Eveenta.—WJ. Sp. 
6 
Fig. 58. 
Fig. 58.—Retzia Hugenia. a,b,c, dorsal, side, and ventral views of a specitnen; d, a smaller 
specimen=dorsal view. 
Description.—Shell small, sub-globular, with from ten to twelve 
strong angular ribs on each valve. Ventral valve convex, most pro- 
minent on the upper half, a slight mesial depression the width of 
three or four of the ribs in the lower half; beak elevated, incurved, 
but not in centact with the umbo of the dorsal valve, perforated at 
the point ; a flat, selid deltidium or area beneath the aperture. Dor- 
sal valve rather strongly and uniformly convex, most prominent along 
the middle, where slight indications of a mesial fold are evident ; 
umbo small, rounded; beak buried beneath the lower edge of the 
deltidium or area of the ventral valve. 
Length of the largest specimen seen, six lines; width about the 
