xxviii SYNOPSIS OF GENERA. 
or by several oblique teeth A Ligament external, contained in a shallow and 
narrow groove along the cardinal border. Muscular scars not strongly impres¬ 
sed, situated below the extremities of the hinge-line. Pallial line simple. 
This genus differs materially from Nucula, Leda. and Yoldia, in the absence of 
a cartilage-pit beneath the beaks; in having an external ligament and a sulcus 
on the post-umbonal slope. It differs from Nuculites in form, and in the absence 
of a clavicular ridge on the anterior end. In general form and internal char¬ 
acters this genus very closely resembles Tellinomya , and it is probable that 
further study will prove that the two are congeneric. 
Examples: Palcconeilo constrida, pi. xlviii, figs. 1-16. 
Pal&oneilo fecunda, pi. xlix, figs. 13, 15-24. 
Paicconeilo attenuata, pi. 1, figs. 34-39. 
Macrodon, Lycett (Murch. Geol. Chelt.). 
Shell equivalve, inequilateral, transverse, sub-elliptical, or sub-ovate in out¬ 
line. Anterior end angular at the cardinal line, rounded below. Posterior 
end rounded or obliquely sub-trunc.ate. Beaks anterior to the middle. Cardinal 
line long and straight. 
Surface marked by concentric striae which are often regularly laminose, and 
in some species by fine radiating striae. 
Hinge furnished with several (sometimes eight) small diverging teeth beneath 
the beak and by from two to four lateral teeth situated near the posterior ex¬ 
tremity of the cardinal line. Ligament external. Muscular impressions not 
strongly marked. Pallial line simple. 
Examples: Macrodon Hamiltonia, pi. li, figs. 1-7, 9, 10. 
Macrodon Chemungensis, pi. li, figs. 11-16. 
* The hinge characters of this genus and the resemblance to the g-enus Neilo were first indicated to me 
by Mr. R. P. Whitfield. 
