91 
De 
think the two species can be generically separated. L. Huronensis is distinguished from L. 
multicostu by its much more elongated and contracted form, the greater convexity of its valves in 
the umbonal region, the much more prominent and strongly incurved beak of the ventral valve, 
the absence of a foramen, the much greater width and shallowness of the sinus and fold, and 
the stronger and more crowded lines of growth. I have not seen any example which exhibits 
the interior. 
Locality and Formation.—Shales of the Hamilton Group, Widder, Township of Bosanquet 
(Collected by Mr. George Jennings Hinde). 
Genus AMPHIGENIA (Hall). 
‘‘ Shell inequivalve, oval, ovoid, or sub-triangular, more or less cenvex or gibbous, with- 
out mesial fold or sinus. Valves articulating by teeth and sockets, without area. The den- 
tal lamellze in the ventral valve conjoined on their dorsal sides, forming an angular trough or 
pit, which opens exteriorly by a triangular fissure beneath the beak, and in its anterior exten- 
sion is supported on a 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 sup- 
porting the crura, which extend into the cavity of the shell’? (Hall, Pal. N. Y. Vol. IV., p. 
382). 
In addition to these characters, there is a foramen which extends beneath the hinge- 
plate of the dorsal valve, and ends in a perforation at the beak, and the shell-structure is dis- 
tinetly punctate. 
Hall has separated the genus Amphigenia from Stricklandinia (Billings) to include the 
single species 4. elongata (= Pentamerus elongatus, Vanuxem), upon the ground that this 
species possesses no area in the ventral valve, with a foramen in the dorsal valve and a punc- 
tate shell-structure. On the other hand, the typical species of Strick/landinia possess an area 
in the ventral valve, a smaller angular pit, no foramen in the dorsal valve, and an impunctate 
and fibrous shell-structure. Without entering further into the controversy which has been 
carried on as regards this question, it may be said that these differences appear sufficient to. 
entitle Amphigenia to be considered as distinct, if not generically, at any rate sub-generically 
from Stricklandinia and Pentamerus. ; 
From Rensseleria, in spite of great resemblance in external form, and also as regards 
some points of internal structure, the genus Amphigenia is separated by the angular pit made 
by the conjoined dental lamellie of the ventral valve, and by apparently having free crura in 
the dorsal valve without appendages. 
The only species of this genus known in Canada, is the Amphigenia elongata of the 
Corniferous Limestone. 
110. AMPHIGENIA ELONGATA (Vanuxem). 
_ Pentamerus elongatus (Vanuxem), Report Third Geol. Dist. New York, p. 132. * 
Meganteris elongatus (Hall), Tenth Report on the State Cabinet, p. 123. 
Rensseleria elongata (Hall), Pal. N. York, Vol. III, p. 453. 
Stricklandinia elongata (Billings), Canadian Journal, Vol. VI., p. 267, figs. 91, 92. 
Amphigenia elongata (Hall), Pal. N. Y., Vol. IV., p. 383, Pl LIX. 
Shell very variable in form, generally elongate oval, sometimes ovate, the length some- 
times nearly twice the width, or the two diameters at other times nearly equal. Sides 
gently curved, or nearly straight ; front pointed, rounded, or sub-truncate ; ventral valve 
convex, in general more so than the dorsal valve, often obtusely carinated centrally in its 
upper half ; the beak incurved over the umbo of the dorsal valve. Dorsal valve less convex 
as a rule than the ventral, often elevated along the middle line in its upper half, and de- 
pressed towards the sides and front. Surface usually smooth, but marked with strong con- 
centric ridges and Jines of growth. In perfect specimens, the surface is stated to exhibit 
regular radiating flattened strie. Length of a small individual eighteen lines, greatest 
width ten lines. Larger individuals range from two to as much as four inches in length. 
