DUMORTIERIA SUBUNDULATA. 
259 
DuMOETiEEiA SUBUNDULATA (Bmnco). Plate XLIII, figs. 8 — 10 ; Plate XLIV, 
figs. 10—12 ; Plate XLV, figs. 1—12. 
1879. Haepoceeas PSEUDOEADiosrir, Branco. Unt. Dogger ; Abh. geol. Spez.- 
Karte Elsass-Lothringen, Bd. ii, pi. ii, 
fig. 3 only (not 1, 2, 4 — see pp. 246 and 
254). 
1879. — STOUNDULATTTM, varietat exteene-comptum, Branco. Ibid., 
pi. iii, figs. 4, 5. 
1885. — — varietat exteene-comptum, Haug. Beitr. 
Monogr. Harpoceras ; Neues Jahrbuch 
fiir Mineralogie, &c., Bail. -Band iii, 
p. 663 (pars). 
1885. Ammokites, cf. Aalensis, Quenstedt. Amm. Schwabischen Jura, pi. liv, 
fig. 53. 
1885. — cf. cosTTJLA, Quenstedt. Ibid., pi. liv, fig. 50, only. 
1887. Dtjmoetieeia subundttlata, varietat exteene-compta, Haug. Polymor- 
phidae ; Neues Jahrbuch fiir Mineralogie, 
Bd. ii, p. 136. 
Discoidal, compressed, carinate. Whorls narrow and thin, with slightly 
convex sides, ornamented with direct to sub-direct, ventrally-inclined ribs, which 
are generally distant in the inner whorls, and closely approximate on the outer 
whorl ; but both the size of the ribs and their distance apart vary greatly in differ- 
ent specimens. Ventral area slightly defined, much sharpened, carrying a fairly dis- 
tinct carina, which is slightly crenulated by the radii passing over it. Inner margin 
barely defined, slightly sloping. Inclusion about one-third. Umbihcus flat and 
open, generally marked with coarse, distant ribs. Termination with a short 
lateral, and a very short, bluntly-pointed ventral process. Sutures very simple, 
superior lateral lobe short, inner lobes very little dependent. 
This peculiar and variable species is easily recognisable by its combination of 
evolute whorls and great compression — a combination somewhat unusual. It is, 
however, hard to define the species or to say how it differs from others just because 
of its variability, chiefly in the matter of ribbing. Hardly two specimens are alike. 
One form commences with coarse, and ends with fine, closely-set ribs ; another 
has a stage of closely-set ribs preceding the coarse-ribbed period ; another has its 
coarse ribs, but they are set nearly twice as close together ; another has fairly 
fine ribs throughout ; and yet another form has fine, very closely-set ribs during 
all its growth. 
The forms with coarse ribs might, if deprived of their outer whorls, be mis- 
taken for the young Dum. costula ; but their ribs are not so distant. The fine- 
ribbed forms are somewhat like Bum. Moorei ; but they have ribs and not the 
