262 
PALEONTOLOGY OF NEW YORK. 
Genus AMPHIGENIA, Hall. 1867. 
PLATES LXXIU, LXXIV. 
1842. Pentamerus, Vanuxem. Geology of N. Y. ; Kept. Third Dist., p. 131, fig. 1. 
1843. Pentamerus, Hall. Geology of N. Y. ; Kept. Fourth Dist. ; Table of Organic Remains. 
1857. Meganteris, Hall. Tenth Ann. Kept. N. Y. State Cab. Nat. Hist., p. 123, figs. 1, 2. 
1859. Rensselceria, Hall. Twelfth Ann. Kept. N. Y. State Cab. Nat. Hist., p. 38. 
1859. RensselCBria, Hall. Paleontology of N. Y., vol. iii, p. 453. 
1861. Stricklandinia, Billings. Canadian Naturalist and Geologist, vol. vi, ji. 267, figs. 91, 92. 
1863. /Stricklandinia, Billings. Geology of Canada, p. 371, fig. 390. 
1867. AmpJiigenia, Hall. Twentieth Ann. Kept. N. Y, State Cab. Nat. Hist., p. 163. 
1867. Amptiige?iia, Hall. Paleontology of N. Y., vol. iv, pp. 374, 382-384, pi. IviiiA, figs. 21-27; 
pi. lix, figs. 1-11. 
1868. Stricklandinia, Meek and Wokthbn. Geological Survey of Illinois, vol. iii, p. 402, pi. viii, fig. 1; 
pi. ix, fig. 5. 
1874. Amphigenia, Billings. Canadian Naturalist and Geologist, vol. vii, second sei-., p. 240. 
1879. Amphigenia, Ratiibun. Proc. Boston Society Nat. Hist., vol. xx, p. 34. 
1885. Amphigenia?, QUhlert. Annales des Sciences Naturelles, vol. xii, p. 8 (author’s ed.), pi. xii, 
figs. 5, 6; ]il. xiii, figs. 7-9. 
“ Shells inequivalved, oval, ovoid or rectangular, more or less convex or gib¬ 
bous, without mesial fold or sinus. Valves articulating by teeth and sockets, 
without area. The dental lamellae in the ventral valve conjoined on their 
dorsal [ventral] sides, forming an angular trough or pit, which opens exteriorly 
by a triangular fissure beneath the beak, and in its anterior extension is sup¬ 
ported on the central septum. Dorsal valve with a strong thickened cardinal 
process or hinge-plate, bordered by the teeth sockets, anchylosed to the bottom 
of the valve and supporting the crura, which extend into the cavity of the shell. 
“ In all the specimens examined there is a foramen extending beneath the 
hinge-plate, and ending in a perforation at the beak. The shell-substance is 
distinctly punctate, and, in exfoliated specimens, presents a prismatic structure. 
So far as known, the crura terminate in slender extensions, without appendage 
of any kind.” (Hall, loc. cit.) 
Type, Pentamerus elongatus, Vanuxem. Corniferous limestone. 
Amphigenia is a remarkable genus. Retaining the striking external contour 
of Renssel^ria, a terebratuloid, its punctate shell-structure, and the same 
arrangement of muscular scars, it differs from that genus in the persistent 
development of a spondylium in the pedicle-valve, and of long, discrete crural 
processes in the brachial valve. These differences are apparently slight, but 
they involve important considerations, and are of themselves a demonstration 
of the close genetic relation between the pentameroids and terebratuloids; at 
