140 THE DEVONIAN FOSSILS OF CANADA WEST. 
tute of an aperture in the ventral valve, but it now turns out that 
many of them have a small circular perforation in the beak. Some 
are therefore disposed to reject the name Athyris (which means 
“ without a door;” or, ‘deltidium,” as Mr. Woodward construes it) 
altogether as inappropriate ; and accordingly D’Orbigny, in 1847, re- 
described the genus under the name of Spirigera. His description is 
in substance the same as that of McCoy, but more m detail, and, 
with the additional character, that the ventral valve is truncated at 
the beak by a circular orifice.* This would exclude more than half 
the species that he placed in his genus; as all those which belong to 
the group typified by A. tumida, A. Ceres, A. passer, &c., have the 
beak entire. With respect to this part of the shell, therefore, D’Or- 
bigny’s definition is quite as defective as McCoy’s. 
In 1851, Professor Suess, of Vienna, proposed the name af Merista 
for some of these shells, but did not define his genus nor give the 
names of any species to be included in it.+ 
In 1852, McCoy, in the 2nd Fasciculus of the “ British Paleozoic 
Fossils,’ page 196, re-defined Athyris as follows :— 
‘“ Gen. Ch—Nearly orbicular or ovate, both valves convex; no cardinal area, 
foramen, or hinge-line ; spiral appendages to beak of entering valve very large, 
nearly filling the shell; a strong mesial septum in the rostral part of entering 
valve ; dental lamelle moderate ; tissue of shell apparently fibrous. 
‘One specimen [of A. ¢wmida] shews the pallial and ovarian impressions to 
be thick, numerous, and dichotomising frequently from beak to margin.” 
Afterwards, in 1854, Suess objected to the term Athyris being ap- 
plied to sach species as 4. twmida, on the ground that it was origin- 
ally used to include Spirigera eoncentriea, S. lamellosa, and other 
similarly organized forms.t He therefore proposed to suppress 
Athyris altogether, substituting Spzrigera for those with the beak 
perforate, and his own genus Merista for the others with entire beak, 
or mesial septum in the dorsal valve and a shoe-lifter process in the 
ventral. It is quite certain now, however, that some of those with a 
non-perforate beak have no shoe-lifter process, and cannot be included 
in Merista. 
In Davidson’s “ Introduction, on the Classification of the Brachio- 
poda,” Spirigera is retained for those with the beak perforate, and no 
* Paléontologie Francaise, vol. iv. page 857. 
t Jahybuch der K. K. Geologischen Reichanstalt, Vienna, ii. pt. 4, pp. 150, 160. 1851. 
ft This is taken from a note by Mr. Davidson, on page 4 of the Appendix to. his British 
Oolitic and Liasie Brachiopoda. 
