252 PALEONTOLOGY OF NEW YORK. 



Gkncs AMPHIGENIA, Hall. 1867. 



PLATES LXXIU, I.XXIV. 



1842. PtHtaiHcnu, Vakoxem. Geology of N. Y. ; Rept. Thiiil Dist., p. 131, fig. 1. 



1848. PenUiinenut, Hall. Qeolog-y of N. Y. ; Rept. Fourth Dial. ; Tablf- of Organic Remains. 



1867. Meganteris, Hall. Tenth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 123, figs. 1, 2. 



1859. Hetutelmria, Hall. Twelfth Ann. Rept. N. Y. State Cab. Nat. Hist., p. 38. 



1859. RetisnelariOy Hall. Palteontology of N. Y., vol. iii, p. 453. 



1S6I. Stricklatidinia, Billikos. Cana<lian Naturalist ami Geologist, vol. vi, p. 267, figs. 91, 93. 



1863. Stricklandinia, Billings. Geology of Canada, p. 371, fig. 890. 



1867. Amphigenia, Hall. Twentieth Ann. Rept. N. Y State Cab. Nat Hist., p. 163. 



1867. Amp/iigenia, HAhh. Paleontology of N. Y., vol. iv, pp. 374, 382-384, pi IviiiA, figs. 21-37; 



pi. lix, figs. 1-11. 



1868. Stricklaiuiinia, Mbbk anil Worthkn. Geological Survey of Illinois, vol. iii, p. 402, pi. viii, fig. 1; 



pi. ix, fig. 5. 

 1874. Amphigenia, Billikos. Canadian Naturalist and Geologist, vol. vii, second ser., p. 240, 

 1879. Amphigenia, Rathbun. Pi-oc. Boston Society Nat. Hist., vol. xx, p. 34. 

 1885. Amphigeniaf, QS.Hi.jmT. Annales des Sciences Natnrellep, vol. xii, p. 8 (author's ed.), pi. xii, 



tigs. 6, 6 ; pi. 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, he. cit.) 



Type, Pentamerus elongaius, Vanuxem. Corniferous limestone. 



Amphigenia is a remarkable genus. Retaining the striking external contour 

 of RENSSELiGEiA, 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 



