Foerste.] 
322 
LMay 1, 
.55 of the breadth. The greatest convexity of the valves is near the 
cardinal margin and there are indications of a mesial fold. Placing 
this form as a variety under S. lens it will represent the opposite 
extreme. In our American Clinton fossils we have several forms 
that may be considered as filling the gap. 
In the collections from Cumberland Gap, Tennessee, there are 
ventral valves which approach variety microcamerus. One of these 
is 18 mm. long, 29 mm. broad and 3.2 mm. deep. It has a very 
shallow mesial depression, and several irregular radial elevations, 
broad, flat, and indistinct. The curvature of the shell antero- 
iposteriorly is quite regular. The other specimen is 13.7 mm. long, 
22 mm. broad, and 2.2 mm. deep. It has a fairly distinct mesial 
depression, and several indistinct radial raised patches on the rest 
of the valve. Two dorsal valves of a very different type occur. 
They are both gently curved except near the cardinal margin where 
the curvature is decidedly increased. One specimen is 22 mm. long 
and 22 mm. broad, with a depth of 3.2 mm. The other is 24 mm. 
long and of about the same width. They are both casts of the 
interior and show the muscular scars well. In general the length 
of the shell increases with age, forms 13.3 mm. long having a length 
equal to .87 the width, forms 21 mm. long having a length equal 
to .93 the width of the dorsal valve. 
At present the discrepancy between the measurements of the 
dorsal and ventral valves of the Tennessee specimens cannot be 
accounted for, they never having been found connected. 
In his Catalogue of Silurian fossils of Anticosti, Billings cited 
S. lens , Sowerby, but this was subsequently found to be an error 
and Strielclandinia brevis became the name of the Anticosti spec- 
imens. Stricldandinia Saltern , Billings, also of Anticosti, was de- 
scribed at a later date. In the typical specimen the length is equal 
to .78 of the width, being thus one of the intermediate forms be- 
tween var. microcamerus and the species. In one of the specimens 
at hand the hinge line is 27 mm. long, the length of the shell is 26 
mm., the general width of the shell is 32 mm. and the thickness is 
13 mm. The dorsal valve has a low mesial fold scarcely visible 
along the posterior third of the shell, moderately distinct anteriorly, 
where it is about 10 mm. broad. The ventral valve has a corres- 
ponding depression less distinctly marked. The surface is finely 
striated radially and finely wrinkled— sometimes with a few coarse 
wrinkles — concentrically. 
