LAMELLIBRANCHIA TA. 
163 
strongly marked on the cardinal expansions and over the hinge-margin. 
In well-preserved specimens the undulations are stronger upon the middle 
of the valve, and less marked upon the anterior side and the wing. In the 
right valve they are much more regular and subdued. 
Interior characters unknown. Ligamental area marked by a distinct 
groove parallel to the margin. 
The largest specimen has a length of 50 mm., height 46 mm., hinge-line 
aboui>45 mm. A small specimen measures 26 nim. in length, 39 mm. in height, 
hinge-line imperfect. Another specimen is 26 mm. in length, 33 mm. in 
height, hinge-line 27 mm. A right valve is 33 mm. in length, height about 
the same, hinge-line 41 mm. 
This form resembles, in general surface characters, the three preceding- 
species, but differs by the more erect body and sub-orbicular form. In general 
aspect it resembles Glyptodesma, and the surface markings are not very differ¬ 
ent, though none of the specimens show the hinge characters of that genus. 
The description has been drawn from specimens preserved in fine calcareous 
shale and in coarser arenaceous material, and the characters remain essen¬ 
tially the same in both. 
In a single specimen from the arenaceous shales on the shore of Cayuga 
lake, at Norton’s Landing, where the shell is partially exfoliated, the surface 
is marked by fine, concentric lines of growth, and more distant lamellose striae, 
which are about twice as numerous as in the typical specimens. These give a 
gently undulating character to the surface of the cast of the left valve, instead 
of the abrupt angular folds of the typical specimens. In the right valve of the 
same specimen the striae on the umbo are similar, but more closely arranged, 
and on the lower portion, in the cast, they exhibit the gentle undulations of the 
typical forms of the right valve. 
Formation and localities. In shales of the Hamilton group, in Ontario county; 
Norton’s Landing, Cayuga county; Bellona, Yates county, and in the coarse 
grits at Leonardsville, Madison county, N. Y. 
