SYNOPSIS OF THE GENERA INCLUDED IN THIS VOLUME. 
Modiomorpha, Hall (Preliminary Notice Lamellibranchiata, 2, p. 72. 1870). 
[Type, Pterinea concentrica, Conrad.] 
Shell equivalve, very inequilateral, sub-ovate in outline, largest posteriorly. 
Anterior end rounded, forming a projecting lobe of greater or less extent 
beyond the beak. The valves are crossed obliquely by a more or less distinctly 
defined cincture passing from the beak to the base, and constricting the basal 
margin. Beaks small, compressed. 
Surface of the shell marked by rugose or undulating concentric striae. 
Hinge furnished with a strong wedge-form tooth in the left valve and 
a corresponding cavity in the right. No lateral teeth have been observed. 
Ligament external, attached to the thickened margin of the shell, which is 
often longitudinally grooved for its reception. Anterior muscular impression 
situated within the anterior extension of the shell. Posterior impression large 
and superficial, situated on the posterior slope. Pallial line simple. 
Examples: Modiomorpha concentrica, pi. xxxvi, figs. T-18. 
Modiomorpha mytiloides, pi. xxxviii, figs. 1-16. 
Goniophora, Phillips (Memoirs Geol. Surv. Gt. Britain, vol. ii, pt. 1, p. 264. 
1848). [Type, Goniophora cymbiformis, Sowerby, sp.] 
Shell equivalve, very inequilateral, rhomboidal or trapezoidal in outline, 
obliquely truncate behind and rounded in front. Cardinal line usually straight 
and not oblique. Beaks small, closely incurved, situated within or about the 
anterior third of the shell. Umbo prominent. Umbonal slope continued as a 
