458 
THE GEOLOGIST. 
genus ; and it was this which led Professor M'Coy to designate the group 
by the name of Athyris, the etymology of which would imply a shell 
without a door, or, in more appropriate words, without an opening.* 
It is, however, certain that the larger number of species and specimens 
exhibit a clearly truncated beak and circular opening, so that aU that 
can be inferred is, that the animal could, at some time of its existence, 
or from peculiar causes, dispense with its mooring, and that this was 
caused by the beak becoming so much incurved or adpressed as to leave 
hardly any space for the passage of peduncular fibres. 
In the interior of the large valve the hinge-teeth are supported by 
vertical shelly plates, and the free space on the bottom of the valve 
between and beyond these is filled up with muscular impressions. The 
muscle whose function was the closing of the shell has formed a small, 
elongated, mesial, heart-shaped scar, and under, as well as along the 
outer side are se en the impressions of the cardinal or divaricator muscles 
— that is to say, of those which had the office of opening the shell. The 
impressions of the pedicle or ventral adjuster muscle may also be clearly 
or distinctly seen on either side close to the abductor ; so that the muscidar 
impressions appear to have been very similarly placed in this valve of 
Athyris as in the corresponding one of Terebratula, although no trace 
of the accessory divaricator and capsular, or peduncular, muscle could 
be perceived ; but it is right to observe that these are not always dis- 
tinctly seen even in the Terebratute. 
In the interior of the smaller valve the hinge-plate presents four 
depressions or pits, which afforded attachment to the dorsal pedicle or 
dorsal adjuster muscles, and which served, according to Mr. Hancock, 
to move the shell on the peduncle, and to adjust it. 
This hinge-plate is likewise perforated close to its summit (under the 
umbone) by a minute circular aperture, which in some species has been 
seen to communicate with a small cylindrical tube, which, after 
originating under the platform, extends longitudinally and freely, with 
a slight upward curve, to about a third of the length of the valve. On 
* The term Cleiothyris had been proposed some years before by Professor 
Phillips for the same liind of shells, but its etymology is liable to the same ob- 
jection as that of Athyris. On the Continent, the generality of authors refuse to 
adopt either of these denominations, and prefer that of Spiriyera, more recently 
proposed by D'Orbigny, and I would willingly adopt this last denomination were 
it not that, both in this particular and many others, naturalists still retain names 
which imply zoological contradictions. 
