XXX 
SYNOPSIS OF GENERA. 
Grammysia, De Verneuil (Bull. Soc. Geol. France, 2d ser., vol. iv, p. 696. 1847). 
[Type, Grammysia Hamiltonensis, De Verneuil, 1847 — Pterinea bisulcata, 
Conrad. 1838. | 
Shell equivalve (with the exception of the alternation of the cincture 
and fold in the two valves, which produces a slight inequality), inequilateral, 
transversely elliptical or sub-ovate. Margins closed. Beaks prominent and 
incurved, situated anterior to the middle. Cardinal line straight or somewhat 
arcuate. Escutcheon and lunule well defined. Valves, in the typical forms, 
traversed from the beak to the base by an oblique cincture and adjacent fold, 
which may be duplicate, and are alternating in the two valves, sometimes pro¬ 
ducing a constriction and short extension of the ventral margin. Some species 
show the cincture developed in the upper part becoming obsolete before reach¬ 
ing the margin. Many forms show a broad cincture without an adjacent fold ; 
and in some species the cincture is indicated by a line of slight interruptions 
or irregularities in the concentric undulations; other species have the surface 
continuous, without cincture or fold. 
Surface marked by concentric striae of growth, and often by strong concen¬ 
tric undulations. Many species also show fine pustulose radiating striae. 
Hinge-plate short and strong, with one or two thickened folds beneath the 
beak of some species. Ligament external, closely resembling that of Unio. 
Anterior and posterior muscular impressions faintly marked, the latter much the 
larger. Pallial line simple, often broken into pits and furrows. 
The above description is emended to include cingulate and smooth forms. 
It has been found that the cincture is a very variable character even in the 
same species, and that no generic line can be drawn between species having a 
well-developed cincture and those in which this feature is obsolete. 
This genus as properly limited will be found to include many species hereto¬ 
fore referred to Allorisma, Sanguinolites, Orthonota, Ch&nomya, etc. 
Dr. L. G. de Koninck has lately (Faune Calcaire Garb de Belgique, pt. v, p. 
4. 1885)* referred most of the species heretofore regarded as Grammysia to the 
* The letter press of the descriptions of species of this volume was all in type before Dr. de Koninck s 
publication was received, and hence no references or comparisons of species could be made. 
