144 THE DEVONIAN FOSSILS OF CANADA WEST. 
of the valve, and the dental plates are partly supported by it. I 
think this process is an abnormal form of the pseudo-deltidium, that 
occurs in some of the Spirifers. 
In all of the genera, Spirifera, Cyrtia, Spiriferina, Suessia, 
Cyrtina, Athyris, Spirigera, Merista, Nucleospira, and Uncites, the 
spiral appendages have the apices of the cones which they form 
directed outwards, towards the sides of the shell, as represented in 
the following figure, 51. 
Fig. 51. 
Fig. 52. Fig. 53. 
Fig. 51. Interior of Athyris (Spirigera) ambigua, showing the disposition of the spiral 
appendages. Copied from Davidson.—(Geologist, Vol, III. Plate 1. 
Fig. 52. Interior of ventral valve of Spirigera concentrica shewing the muscular impres- 
sions and the circular aperture in the beak. 
Fig. 53. Interior of ventral valve of Merista Herculea (Barrande), a Bohemian species, S.— 
the shoe-lifter process. D.—the divaricator muscular impressions. 
It will be seen on examining fig. 51 closely, that the first coils of the 
spiral appendages are connected on the dorsal side by a transverse bar, 
from which an upright process springs, sloping upwards slightly 
towards the beak, and giving off two half coils,—one on each side. It 
