321 
[Foevste. 
valves is such that the anterior portions of the same in the com. 
plete shell must have met at an angle more or less acute, especially 
along the median lobes. The posterior half of the margin on either 
side of the beak is more or less straightened, sometimes giving a 
sort of triangular appearance to the shell. Length of an ordi- 
nary sized individual, 7.1 mm. ; width 8.2 mm. 
We fail to find any satisfactory American form with which to 
associate these specimens and Rhynchonella decemplicata of the 
Upper Llandovery possesses at least the advantage of being an 
old and well recognized species from a somewhat similar horizon. 
Rhynchonella bidens , Hall, is a smaller species, and more ventricose. 
Rhynchonella Whitii, Hall, of the Niagara, has a more sharply ele- 
vated mesial fold, and more angular plications. Those found in 
the Lower Helderberg and usually associated with Rhynchonella 
formosa , Hall, have also a more elevated mesial fold. More spec- 
imens are needed to decide their identity with the British species. 
A small specimen was found at Cumberland Gap, presumably 
of this species, 4.8 mm. long, and 5.3 mm. broad. The five plica- 
tions of each lateral lobe are almost obsolete, only the inner one or 
two plications of each lateral set being at all readily seen. The 
two plications of the median lobe, scarcely distinguishable for two- 
thirds the length of the shell, along the anterior third become very 
prominent and project boldly beyond the margin of the lateral 
lobes. 
Rhynchonella Salteri , Davidson, has some features comparable 
with this specimen. Hall figures from Waldron, Indiana, under 
Rhynchonella Indianensis , Hall, a specimen which is still more like 
the Tennessee form. The Tennessee form, as already stated, is 
probably the young of the larger specimens previously described. 
Stricklandinia lens, Sowerby. 
(PLATE V, FIGS. 1-4.) 
Stricklandinia lens in its typical form has the cardinal margin 
of the dorsal valve straight, about five-eighths of the width of the 
shell, the lateral margin making angles of about 120° with the car- 
dinal margin. The beak of the ventral valve is fairly elevated, the 
posterior margin of the valve being in consequence curved. It 
represents one of the largest of the species of which it is a type. 
Pentamerus microcamerus , McCoy, is a smaller form, with a 
relatively much shorter length ; the length being said to equal only 
PROCEEDINGS B. S. N. H. VOL. XXIV. 21 DECEMBER, 1889. 
