236 Mr. E. Billings on the Genus Athyris. 
dorsal [ventral] valve. 2. Martinia, M‘Coy, or the smooth Spirifers, 
in which the hinge-line is less than the width of the shell, and the 
cardinal area triangular. 3. Athyris, M‘Coy, in which there is no 
vestige of either foramen, cardinal area, or hinge-line. This remark- 
able genus is frequently confounded with those shells usually named 
Terebratula in the older rocks, but is distinguished by the large 
spiral appendages, which are wanting in the other group. 4. Bra- 
chythyris, M‘Coy, in which we find the longitudinally ribbed sur- 
face of Spirifera united with the short hinge-line of Martinia. 
5. Orthis, Dal., in which there are no spiral appendages, the hinge- 
line and strize frequently spinose (as in Leptena), the cardinal area 
common to both valves, and its sides inclined towards each other 
at its angles; dorsal valve smallest.’’—Op. cit. p. 128. 
On page 146 of the same work he thus concisely describes 
the genus :— 
** Gen. Char.—Nearly orbicular, small; no cardinal area or hinge- 
line ; spiral appendages very large, filling the greater part of the 
shell. 
«This very interesting group possesses all the external characters 
of the Terebratulide united to the internal structure of the Spirifers, 
to which latter family it truly belongs. Prof. Phillips is the only 
author who has recognized the group: he forms of it his last division 
of the genus Spirifera, but gives no characters to distinguish it from 
Terebratula; the internal structure is, however, a sure guide.”’ 
The above is all that he wrote about the genus at that time; 
and it will be perceived that he does not point out any parti- 
cular species as the type, and, further, that there is nothing in 
his remarks from which it can be inferred that he knew any- 
thing about the genera into which the group was afterwards 
subdivided. Consequently it is impossible that he could have 
intended to confine the genus to any one of them, as is now 
affirmed by some of the naturalists who are opposed to the clas- 
sification advocated in this paper. Instead of excluding species 
with an imperforate beak such as A. tumida, the etymology of 
the word Athyris (without a door or opening), the expression 
‘‘in which there is no vestige of either foramen, cardinal area, 
or hinge-line,” and also his typical figure, all induce the belief 
that he had before him one or more forms with the beak entire. 
This is rendered certain by what he says on page 147. Speak- 
ing of what he calls A. concentrica, he says :—“ This species is 
not uncommon; it is figured in the ‘ Bull. de la Soc. Géol. de 
France,’ with a perforated beak as in Terebratula. I have, how- 
ever, seen numerous specimens with the beak entire and imper- 
forate, as in the other paleozoic species.” It is highly probable 
from all this that he had in view such Silurian forms as A. tu- 
mida. This latter species is so common that it is almost certain 
pine ia 
a oe eae Se ee 
