STROPHEODONTA. 151 
Secondly, we have eight larger specimens from Lummaton and Wolborough, 
which are steeply geniculated, and coincide with Phillips’s type in every respect. 
These agree with the former set of specimens in character and ornament, except 
that the corrugations are more definite, and there can, I think, be no doubt that 
they are simply its adult condition. 
It seems to me that this species is distinguished from St. rhomboidalis by the 
strie being much closer and lower as well as more numerous and flexuous, 
by the rug being more numerous, more rounded, and lower, and also by other 
particulars more easily recognised than described. One of the specimens shows 
that the internal arrangements are different. 
With the young form of this species Stropheodonta planolata, Hall, seems in 
close agreement, showing in some specimens the same variation in the ribs. 
Stropheodonta perplana, Hall,’ is also very similar in general appearance, and at 
least in some characters. 
St. piligera, Sandberger, also seems from its figures to agree with the young or 
lenticular form of our shell, except that the rays are rectilinear. It is described 
as geniculate in its adult state. The muscular impressions on the upper valve 
seem, however, to be larger. 
2. STROPHEODONTA IRREGULARIS, I’. Romer, sp. Pl. XVII, fig. 1. 
1844. Lepr@Na IRREGULARIS, F. Romer. Rhein. Uebergangsgeb., p. 75, pl. iv, 
fig. 1. 
1884. STrROPHOMENA IRREGULARIS, Davidson. Brit. Foss. Brach., vol. v, p. 285, 
pl. xx, fig. 23. 
1885. _ — Maurer. Abhandl. Grossh. Hessisch. Geol. 
Landes., vol. i, pt. 2, p. 145, pl. 
v, figs. 18—20. 
Remarks.—There is one specimen in my Collection from Wolborough which 
shows the constant divarication of the ribs which is indicated in Rémer’s figure. 
Mr. Champernowne’s fossil is the only one I know from Lummaton. 
3. STROPHEODONTA INTERSTRIALIS, Phillips, sp. Pl. XVII, figs. 3, 4. 
1841. Onruis 1NTERSTRIALIS, Phillips. Pal. Foss., p. 61, pl. xxv, fig. 103. 
71843. SrropHOMENA VARISTRIATA, Oonrad. Journ. Acad. Nat. Sci. Phil., vol. 
vill, p. 255, pl. xiv, fig. 6. 
1854. - z1azaG, Sandberger. Verst. Rhein. Nassau, p. 365, pl. xxxiv, 
fig. 7. 
21859. — varistriata, Hall. Pal. N. Y., vol. iii, p. 180, figs. 1—8, 16. 
1 1867, Hall, ‘ Pal. N. Y.,’ vol. iv, pt. 1, p. 92, pls. xi, xii, xvii, xix, passim. 
