ZURCHERIA PERTINAX. 
297 
ZuECHEEiA INCONSTANS, 8. Buckman. Plate L, figs. 4 — 10. 
Discoidal, compressed, uncarinate. Whorls elliptical, at first smooth, then 
showing small spines, presently with ribs inside the spines, and lastly ornamented 
with subdirect ventrally-inclined costge. Ventral area narrow, uncarinate, not 
defined, crossed by arcuate growth-lines. Inner margin fairly defined, smooth. 
Inclusion about one-third. Umbilicus open, inner whorls smooth. Suture-line 
fairly ornate ; siphonal saddle divided by a small accessory lobe ; superior lateral 
lobe trifurcate ; superior lateral saddle deeper than siphonal saddle ; inferior lateral 
lobe nearly as long as superior lateral, very unequal-sided ; inferior lateral saddle 
very shallow ; one well-marked auxiliary lobe a little dependent. 
This species is the further development of Zurcheria parvispinata. It is more 
compressed, the spinous stage ends earlier, and the costate stage eventually becomes 
somewhat less pronounced. The smaller specimen is evidently a little more 
advanced, biologically than the larger one. 
In the smaller specimen the spines appear before the ribs are distinct ; and this 
is probably due to modifying action of earlier inheritance. That the later feature, 
the spines, should remain is probably due to the fact that they had persisted long 
enough to become a fairly fixed character, and then " modifying action " would 
reduce all ornaments equally, and the ribs, being smaller, would disappear first in 
the inner whorls. 
The larger specimen is the first example of the genus which I obtained. This 
was some few years ago ; and I labelled it as a " Harpoceras without a keel." 
Both specimens came from the Goncavum-zone of Bradford Abbas, Dorset ; and 
they are the only specimens of this rare species which I have seen. Figs. 4, 5, 6 
of PI. L give three views of the smaller example, a very well-preserved fossil 
with test ; fig. 7 is part of its suture-line. Figs. 8, 9 of the same plate exhibit 
two views of a specimen without test ; and fig. 10 shows the characteristic 
suture-line. 
ZuRCHBETA PEETiNAx (Vacek). Plate XLIX, figs. 21, 22. 
1886. Ztjrcheeia Ubaldi ? Haug. System. StellungZwrcAerm; Neues Jahrbuch 
fiir Mineralogie, &c., Bd. ii, p. 194, figs. 1 — 3. 
1886. Hammatoceeas peetinax, Vacek. Ool. Cap San Vigilio ; Abh. k. k. 
geol. Eeichsanstalt, vol. xii, pi. xvi, 
figs. 5—7. 
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