SYNOPSIS OF GENERA. 
xiiii 
lunule. The species are closely allied to Pholadella, and when more forms 
become known it may prove convenient to unite the two genera. In some 
important points the genus approaches to Grammysia by the way of Allurisma. 
The marked external ligamental area and strong lunule are common to the 
three genera, while the surface markings have many points in common. In 
the absence of critical knowledge of the hinge structure we are unprepared to 
make any more positive assertion regarding this genus and its allied forms. 
Examples: Cimitaria recurva, pi. lxxvii, tigs. 9-14. 
Cimitaria elongata, pi. lxxvii, tigs. 5-8. 
Cimitaria corrugata, pi. lxxvi, figs. 1-4. 
Pholadella, Hall (Prelim. Notice Lamellibranchiata, 2, p. 63. 1869-70). 
[Type, Pholadella Newberryi.] 
Shell equivalve, inequilateral, transversely elongate, ovate, sub-elliptical or 
trapezoidal. Anterior end rounded or obliquely truncate. Posterior end trun¬ 
cate. Beaks much in advance of the middle of the valve, closely incurved. 
Umbones prominent. Cardinal line straight. Umbonal slope prominent, 
rounded or sub-angular. Cardinal slope flat or sub-alate. 
Surface marked by fine concentric striae, and partially by strong concentric 
undulations, which may be confined to the anterior portion or extend over the 
body of the shell. Distinct radii, originating at the umbo, mark the central 
and often the greater portion of the body, leaving the anterior end and cardinal 
slope free from this ornamentation. 
The cardinal margin is marked by a strong cartilage groove, and the anterior 
end by a deep and sharply defined lunule. The characters of hinge-teeth, and 
muscular impressions have not been determined. 
The typical form of this genus bears many characters of the genus Cimitaria , 
and others are closely allied, by external form, to Gram?nysia. Indeed so 
close is this external relation that one species of the latter genus, having an 
elongate form and somewhat peculiar surface markings, has been referred to 
the genus Pholadella. Three well-defined species are illustrated in this volume. 
