378 BRITISH PALAZOZOIC FOSSILS. { Bracutopopa. 
Genus. ATHYRIS (M*Coy). See page 196. 
Atuyris CoNCENTRICA (V. Buch Sp.) 
Ref. and Syn. = Terebratula concentrica V. Buch, Bul. de la Soc. Geol. de France, Vol. XI. t. 2.f.1.= Atrypa 
decussata Sow. G. T. 2nd Series, Vol. V. t. 54. f. 5. + A. hispida Sow. same plate f. 4.+ A. oblonga id. id. 
t. 53. f. 6. (crushed internal cast I find). 
Sp. Ch.—Suborbicular when young, becoming rhomboidal or subpentagonal when old; valves almost 
equally convex, increasing in gibbosity with age; sides rounded ; front evenly rounded in small specimens, but 
after seven lines long becoming produced into a broad lobe, which at an inch in length becomes a deep 
elliptical sinus, forming an undefined rounded elevation in the entering valve, and a wide concave sinus in 
the receiving valve, disappearing at about halfway to the beak; beak tumid, incurved, without trace of hinge- 
line or cardinal area, but slightly angulated on the sides; surface marked with close, imbricating, regular 
laminze of growth, about five in one line at three lines from the beak of entering valve, between each of 
which in some specimens appear two or three finer ones; towards the margin of old specimens some of the 
laminze become rugged and more prominent than the rest; and all, when finely preserved, project in fringe- 
like laminze from the shell, which exhibit longitudinal or radiating furrows, and decompose in fringe-like lines 
and points. Length of small specimen (without mesial furrow) five lines, width the same, proportional depth 
of both valves =, width of old specimen one inch, proportional length of receiving valve =, of entering valve =, 
depth of both valves , but varying considerably. 
On examining typical specimens, figured and described by Mr Sowerby from the limestone of S. Petherwin, 
] find the decussation he alludes to is only produced by the decomposition of certain of the concentric laminz, 
in radiating lines, according with their original fibrous texture, and it is not visible in sound specimens. The 
original specimen of his Atrypa hispida, from the shale of the same locality which I have examined, is mani- 
festly the same species as his A. decussata, with one of the decomposing concentric laminze not quite broken 
off, but supported on a lamina of the shale: finally, on comparing both with young specimens, and the rostral 
portion of old specimens of the Terebratula (Athyris) concentrica (Von Buch) from the Eifel, I am able to 
state their positive identity. The edges of the lamine of Eifel specimens of the A. concentrica shew the 
longitudinal striation as well as any of the Devonshire ones, The Spirifer (Martinia) lineata of the carboniferous 
limestone is distinguished by its thicker and more obtuse concentric laminz, greater width, cardinal area, 
and hinge-line. 
Position and Locality—Very common in the slate and subordinate limestone of S. Petherwin and 
Lanlake, Launceston ; brown grits of Barnstaple. 
Genus. SPIRIGERINA (D’Orb.) See page 197. 
SPIRIGERINA DESQUAMATA (Sow. Sp.) 
Ref. and Syn. = Atrypa desquamata Sow. Geol. Trans. 2nd Series, Vol. V. t. 56. f. 19 to 23. 
Sp. Ch —Ovate or subquadrate, nearly orbicular, and subequivalye when young, with a straight hinge-line, 
considerably less than the width of the shell; with age the outline becoming more quadrate, the front slightly 
narrowed, and very slightly elevated towards the entering valve in a wide, shallow sinus, not producing a ridge 
on the entering valve, or a sinus in the receiving valve; entering valve deeper than the receiving one, broadly 
gibbous along the middle, gradually arching to the margins; receiving valve moderately convex in all the 
middle portion, (a narrow portion very slightly concave towards the front lateral margins in old specimens) ; 
lateral margins nearly horizontal, slightly sigmoidal; cardinal area flat, triangular; aperture rounded, close 
under the pointed beak of the receiving valve, separated from the hinge-line by a large bipartite deltidium, 
the dividing fissure of which is often open in young specimens; surface of both valves radiated with close, 
rough, subequal, radiating ridges, separated by narrower, very deep sulci, the ridges increasing in number by 
intercalation, at about four lines from the beak; both the mesial and lateral ones usually dichotomising 
