311 
[Foerste. 
ventral valve which are rather sub-quadrangular, and the concavity 
of the anterior portion of the ventral valve. 
At Hanover, Indiana, specimens are found of two forms. In the 
first form the striae are coarse and distant. The dorsal valve is 
moderate convex, and the ventral is depressed anteriorly or even a 
very broad and very shallow sinus is formed. In the second form 
the striae are not so coarse and are less distant. The dorsal valve 
is more convex, and the ventral valve is moderately convex or flat- 
tened anteriorly. Specimens of the first form are about 25 mm. 
wide and 20 mm. long. Those of the second form are somewhat 
smaller. The muscular scars of the ventral valves of both forms 
are of the Orthis calligramma type, but the anterior margin of these 
scars is often more prominent and sharply defined than in speci- 
mens heretofore seen. The muscular impressions of the dorsal valve 
resemble those of the New York forms. 
The first form of the Collinsville, Alabama, specimens, is also 
found at the Soldiers’ Home Quarries near Dayton, Ohio, where 
specimens 43 mm. in breadth are seen. The dorsal valve is but 
very moderately convex and has a mesial depression or shallow si- 
nus as in the Indiana specimens, but the ventral valve is always 
strongly convex, especially toward the beak, which is curved. This 
is also placed under Orthis calligramma. The species is therefore 
seen to be very variable. We find the flattening of the ventral 
valve a very common variation and where several varieties occur 
these forms are apt to be easily connected by intermediate stages 
with those with strongly convex valves. There is a similar varia- 
tion of the convexity in the dorsal valve which is apt to be con- 
nected with the development of a shallow mesial sinus. The 
angularity of the postero-lateral margins is also very variable. The 
muscular scars of the ventral valve and the fact that ventral valves 
are never concave are the only constant features. For those with 
flattened ventral valves, — including Orthis Jlo.bellulum, Hall, Pal. 
N. Y., Yol. ii, PI. 52, fig. 6, of New York, the second form 
described from Collinsville, Alabama, the first form (plate iv, figs. 
4, 5), and perhaps, also, the second form described from Hanover, 
Indiana — we suggest the name Orthis calligramma var. Jlabellites. 
This may be the species indicated by Orthis jlabellites, Hall, 20th 
Regents Rep. N. Y. State Cabinet, but we do not know. Interme- 
diate forms connecting the variety with the species are not infre- 
quent, as already suggested. 
According to our conception of the species, Orthis calligramma 
