DAVIDSON — ON SOME FOSSIL BRACHIOPODA. 
459 
the bottom of the shell, divided by a small longitudinal ridge, may be 
clearly seen the impressions left by the adductor longus anticus of Ovp^en 
(anterior occlusor of Hancock) ; but those of the posterior occlusor could 
not be distinctly seen on any of the valves that have come under my 
examination. It is probable that the occlusor muscle had four attach- 
ments in this valve, as in Terebratula and other genera. On each side 
of the hinge-plate above described, and of its aperture, exists a pro- 
longed testaceous plate, situated at a higher level, and forming the 
ledge or rim of the inner socket-walls. These two prolongations 
first close to the sockets {b). then follow in the direction of the bottom 
of the valve (o, c) to become recurved again, and thus producing the 
first of the seven or eight convolutions of which each cone is composed. 
From the first two spiral lamelte spring up perpendicularly other two 
secondary ones (o, d), which, by being bent, become united towards the 
middle of the shell (d) between the two spiral cones, and afterwards 
form but a single branch (from d toe). This last, after having attained 
the upper level of the spire (at e) becomes again bifurcated, and forms 
other two lamella3 (/) recurved in half-circle, and terminating back- 
wards by a free extremity (ff) between the first and second coil of each 
spiral cone. 
Such, at least, are the dispositions of the spiral and other parts 
in Athyris pectinifera, and are probably the geceral dispositions of 
become lengthened, and give 
origin (while serving as points 
of attachment) to the two 
lamellse (a), which, by their 
convolutions on either side, 
constitute the spires, as well 
as the intermediate process by 
which theyare united. Thespi- 
ral lamellaa, disposed vertically 
to the plane of the valve, con- 
verge at first, then bend sud- 
denly upon themselves, at a 
short distance from their 
origin, outwards and back- 
wards (5) in the shape of a 
half -circle, which, passing 
2 L 2 
