150 DEVONIAN FAUNA. 
as in older shells. The radiating threads are distant, prominent, and compara- 
tively coarse. 
5. Genus.—StroppHeoponta, Hall, 1852. 
These shells have, in each valve, cardinal areas which are smooth or finely 
striated transversely, sometimes showing denticulations articulating with pits in 
the opposite valve. Tbe muscular area is not limited by a ridge in front. 
The foramen is obsolete. 
1. SrropHeoponta Noputosa, Phillips, sp. Pl. XVI, figs. 6—10. 
1841. Leprmna noputosa, Phillips. Pal. Foss., p. 56, pl. xxiv, fig. 94. 
1854. SrropHoMENA PILIGERA, Sandberger. Verst. Rhein. Nassau, p. 36, pl. 
xxxiv, fig. 10. 
?1859. SrropHoponra PLanouaTa, Hall. Pal. N. Y., vol. ili, p. 184, pl. xvi, figs. 
9—12. 
1882. STROPHOMENA RHOMBOIDALIS, var. NODULOSA, Davidson. Brit. Foss. Brach., 
vol. v, pt. 1, p. 52, pl. iii, fig. 15. 
Localities—From Lummaton twenty-six specimens are in my Collection ; and 
from Wolborough one in my Collection and three (including one figured by 
both Phillips and Davidson) in the Museum of Practical Geology. 
Remarks.—I feel obliged in this instance to differ from Davidson, and to follow 
Phillips in regarding his species as distinct. All the specimens I have seen are 
widely different from St. rhomboidalis, and there is no passage between them. 
It appears to me that the shell was lenticular when young, and only became 
geniculated when old. 
In the first place, among the specimens above enumerated there are a number 
of flat shells, frequently much injured, but all showing the same characters. They 
are covered with multitudinous, minute, and very flexuous, rounded threads, which 
are sometimes discontinuous. In most instances, but not always, every fourth or 
fifth thread is rather larger than the rest. The part about the umbo is very 
slightly convex, and the umbo itself slightly projects beyond the hinge-line in a 
sharp triangular apex. The hinge-line is straight, and as long as the width of the 
shell. The cardinal angles are sharp, and are occasionally produced into a small 
acute wing. The area is narrow, oblique, and striated transversely ; and there 
is a convex pseudo-deltidium. The inner surface of the valve is minutely pitted. 
In most specimens there are more or less distinct indications of rounded corru- 
gations on the surface. These shells I take to be the young form of the species. 
