434 BRITISH PALALOZOIC FOSSILS. [ Bracuiopopa. 
occasionally appear double from a slight decortication. wee of rather large species one inch eight HUES, 
proportional length of receiving valve ;;, of entering valve 7, depth of entering valve 72, of receiving valve 7. 
This species is most nearly allied to the Athyris glabristria, but wants the mesial fold, which in that 
Species is very prominent; it is greatly more depressed, and the edge, instead of being acute, is remarkably 
obtuse and thickened, except in the very young specimens, often leaving very prominent, concentric, rugged 
waves of growth. 
Position and Locality—Common in the lower carboniferous limestone of Derbyshire; common in the 
lower carboniferous limestone of Kendal, Westmoreland. 
ATHYRIS GLABRISTRIA (Phill. Sp.) 
Ref. and Syn. = Spirifera id. Phill. Geol. York. Vol. II. t. 10. f. 19. 
Desc.—Transvyersely elliptical, or slightly rhomboidal ; lateral margins very slightly sigmoidal, strongly 
raised into a broad, deep, rounded wave in front ; sides rather narrow, semielliptically rounded. Entering valve 
gently and evenly convex, without mesial ridge, except an undefined indication near the margin from the 
elevation of the mesial sinus; beak prominent, pointed. Receiving valve moderately convex, with a broad, 
mesial hollow obscurely defined on the sides, but extending faintly from the beak to the large sinus in the front 
margin ; profile much, and regularly arched, greatest depth about the middle of the length; beak very small, 
depressed. Surface even, covered with obsolete, obtuse, thread-like strize (ten in two lines) and a few incon- 
sponau concentric lines of growth. Width of average peel two inches, jegpaxcione length of receiving 
valve 5, of entering valve %, width of sinus in front margin ;%, depth thereof 4, depth of both valves ~. 
The absence of cardinal area easily separates this fossil from the Spirifera glabra, of which it often assumes 
the form. The internal spiral appendages are very large. 
Position and Locality—Not common in the carboniferous limestone of Derbyshire. 
ATHYRIS GLOBULARIS (Phill. Sp.) 
Ref. and Syn. = Spirifera id. Phill. Geol. York. Vol. II. t. 10. f. 22 
Desc.—Rhombie, rounded, moderately gibbous ; lateral margins obtuse, forming thickened edges at several 
stages of growth; lateral margins nearly straight, front margin raised into a deep rounded sinus, producing 
little or no ridge on the entering valve, but a deep mesial hollow, running distinctly to the apex of the beak in 
the receiving valve. Entering valve evenly gibbous, orbicular when young, without trace of mesial ridge; 
becoming rhombic after half an inch long, with the middle portion corresponding to the sinus in the front 
margin obscurely defined as a rounded ridge by the more abrupt bending down of the sides towards the lateral 
margins; profile very slightly arched, greatest depth about the middle. Receiving valve moderately and evenly 
gibbous, greatest depth at one-third from the beak ; mesial hollow deep, narrow in the rostral portion, gradually 
widening towards the front; beak obtuse, much incurved, with a small rounded perforation at the apex. 
Surface smooth, with numerous, irregular, thickened interruptions of growth; tissue fibrous under the lens. 
Internal cast with a few SH radiating linear impressions. Width of large specimen ten lines, pEavorany 
length of nou valve #4, of entering valve +, width of sinus in front margin ;, depth of sinus =, ea of 
both valves “, length and width of ordinary sized Scotch specimens seven en depth of both valves =, depth 
of sinus in front margin =. 
Several writers refer this species, as a variety, to the Athyris ambigua, but I have seen a considerable 
number of specimens apparently very constant in their characters, and certainly distinct therefrom, by the want of 
sulcus on the entering valve, &c.; it has also been referred to the A. De-Roissyi, but the size is always much 
jess, and the concentric lineation is never fimbriated nor marked with longitudinal striz. 
Position and Locality—Common in the carboniferous shale of Glasgow; common in the carboniferous 
shale of Craige, near Kilmarnock ; rare in the carboniferous limestone of Dalmellington, Ayrshire. 
