BRACHIOPODA. 
5 
1888. Spinfo'a, Calvin. Bull. Laboratory State University of Iowa, jip- 19> 28. 
• 1889. Spirifera, Nbttelroth. Kentucky Fossil Shells, pji. 105-134, pi. vi, vii, viii, ix, x, xi, xii, xiii, 
figs. 36-38; pi. xvii, figs. 36-42; jil. xxvi, figs. 2-5; pi. xxix, figs. 13-16, 25; 
pi. xxxi, figs. 10, 11, 13 ; pi. xxxii, figs. 28-31; pi. xxxiii, figs. 23, 24. 
1889. Spirifei', Beecher and Clarke. Memoirs N. Y State Museum, pp. 75, 77, pi. vi, figs. 1-7, 9-11. 
1889. Spirifera, Whiteaves. Contribulions to Canadian Palaeontology, vol. i, p, 114, pi. xv, fig. 3. 
1890. Spirifera, Worthen. Geol. Survey of Illinois, vol. viii, p. 105, pi. xi, fig. 5. 
1890. Spirifera, Fokrste. Proc. Boston Soc. Nat. Hist., vol. xxiv, p. 313, pi. v, figs. 5, 6. 
1890. Spirifera, Williams. Bull. Geol. Soc. America, vol. i, p. 491, pi. xii, figs. 12, 13. 
1890. Spirifera, Hall. Bull. Geol. Soc. America, vol. i, p. 567. 
1890. Spirifera, Hall. Ninth Ann. Kept. N. Y. State Geologist, xi- 9. 
1891. Spirifera, Herrick. Bull. Geol. Soc. America, vol. ii, xi- 45, pi. 1, fig. 18. 
Shells transversely elongate, rarely produced axially; with or without me¬ 
dian fold and sinus. Hinge-line straight, usually forming the greatest diameter 
of the shell, but in some of the subdivisions of the genus, short and inconspicu¬ 
ous. Cardinal extremities alate, acuminate or rounded. 
Surface covered with granulations, striae, plications or costae, variously 
grouped and which may be present or absent on the median fold and sinus; 
these are crossed by concentric growth-lines which may take the form of 
varices or expanded lamellae, or be modified into fimbriae of simple or compound 
spines. In the subgenera Martinia and Martiniopsis the surface is smooth 
except for the concentric striae. Shell substance fibrous, irnpunctate except as 
below described; in the smooth species the epidermal layer is minutely pitted. 
The pedicle-valve has the umbo more or less elevated over the hinge-line, 
the apex acute, erect or incurved. The cardinal slopes show a slight tendency 
to concavity or excavation, and the median portion of the valve is more or less 
strongly depressed by a sinus. The cardinal area is broad, fiat or incurved and 
its surface is transversely striated; the inner shell-layers bear a series of longi¬ 
tudinal or vertical canals at whose marginal extremities the fibrous tissue is 
produced into a row of denticles, corresponding to a row of pits on the opposite 
valve; thus forming an accessory articulation of the valves. The essential 
articulation is effected by means of stout, simple teeth lying at the marginal 
extremities of the triangular deltidium and supported by dental plates which 
are usually short, but, in rare types, may be produced even to the anterior mar¬ 
gin of the valve The pedicle-passage or delthyrium is usually open. Nor¬ 
mally it is closed by a pair of deltidial plates having the form of scalene tri- 
