Mr. E. Billings on the Genus Athyris. 235 
of knowledge of all paleontologists conversant with the fossils 
of the older rocks, and might be thought superfluous. But the 
question is somewhat complicated, and cannot well be decided 
unless in view of all the circumstances. Besides this, it is one 
upon which any good naturalist is perfectly competent to give 
an opinion although specially engaged in other departments. 
Few of these have access to works on paleozoic fossils; and 
therefore, for the convenience of such as may feel inclined to 
investigate the subject, it is desirable to bring all the facts to- 
gether. 
There is no dispute about the extent of the genera; and there- 
fore the details of the internal characters need not be given. It 
is purely a question of natural-history ethics, if I may be per- 
mitted to use such a term. 
1. History and Extent of the original Genus. 
The original description was published in the ‘ Synopsis of 
the Carboniferous Fossils of Ireland,’ in 1844. From this work 
I shall make some extracts, and shall introduce along with the 
original figure two others to further illustrate the subject. 
Fig. 1. Copy of the original figure given by M‘Coy (without a specific 
name) to illustrate his idea of the general form of an Athyris. 
Fig. 2. Spirigera concentrica, Von Buch. The form is copied from 
Davidson’s Monograph of the British Devonian Brachiopoda, 
pl. 3. fig. 13, Pal. Soc. Mon. for 1862. The right-hand side is, 
in this copy, a little restored, and the aperture im the beak made 
larger than it is in the original figure. 
Fig. 3. Athyris tumida, Dalman. Copied from Davidson’s ‘ General In- 
troduction,’ pl. 6. fig. 73. 
The following extracts are from M‘Coy’s work above referred 
6 — 
“The family Delthyridee appears to be divided into the five fol- 
lowing genera :—1. Spirifera, Sow., composed of those longitudinally 
ribbed species in which the hinge-line is equal to, or exceeds, the 
width of the shell, the cardinal area with parallel sides, the cardinal 
teeth of the ventral valve [now called the dorsal valve} large, spirally 
rolled, and having a triangular foramen beneath the — of the 
16 
