RHYNCHONELLID &. 195 
Genus—Poramponires, Pander, 1830. 
I much regret not to be yet in possession of satisfactory information with reference to 
the internal characters belonging to this genus; all we know upon the subject has been 
already recorded at p. 99 of my “ General Introduction,” and we must look to the Russian 
paleontologists for a complete description of the interior of a shell that occurs so plentifully 
in the Lower Silurian rocks of the north of Russia. 
PORAMBONITES INTERCEDENS, Pander ; var. filosa, M‘Coy. Pl. XXV, figs. 16; 17—19 (?) ; 
Bree, foes. 1, 2,3 (°). 
PORAMBONITES INTERCEDENS, Pander. Beitr. zur Geog. des Wussischen Reiches, p. 2, 
fig. 2, 1830. 
SPIRIFER PORAMBONITES, Von Buch. Beitr. zur Geb. Russl., p. 13, pl. ii, figs. 
4—7, 1840. 
= De Verneuil et De Keyserling. Geol. of Russia, vol. 11, 
p. 131, 1845. 
ATRYPA FILOSA, M‘Coy. A Synopsis of the Silurian Fossils of Ireland, p. 39, pl. iti, 
fig. 28, 1846. 
PORAMBONITES INTERCEDENS ? M‘Coy. British Pal. Foss., p. 212, 1852. 
a= — Salter. Siluria, 2nd ed., p. 544, 1859. 
— #aurirostris, D’ Hichwald. lLetheea Rossica, Ancienne Période, vol. i, 
p. 794, 1859 (not P. equirostris, Schlotheim, sp.). 
Spec. Char. Subpentagonal, nearly circular, and either a little longer or shorter than 
wide; greatest breadth about the middle; sides rounded; hinge-line straight, less than 
half the width of the shell, and forming an obtuse angle with the lateral margins. Both 
valves are very convex, the dorsal one being the deepest. Dorsal valve posteriorly 
uniformly convex to about half the length of the shell; the fold, which is moderately 
broad, is slightly rounded, and of small elevation; it occurs on the anterior half of the 
valve ; arearudimentary. Ventral valve with a concave sinus, which extends from the front 
to about half the length of the shell ; beak incurved, area small, triangular, with a fissure 
in the middle. Surface of both valves marked by numerous thread-like radiating striz, 
some of which being closer than others, increase in number as they near the margin 
by the interpolation of shorter ones. These strize are chiefly formed by rows of small 
rounded or oval cells, close to one another, and separated only by narrow ridges ; the free 
interspaces between each longitudinal row of pits or cells are smooth, and of smaller or 
greater width. 
Length 16, width 17, depth 12 lines. 
Obs. M. de Verneuil has justly observed, in his description of Spirifer porambonites 
