396 
INFERIOR OOLITE AMMONITES. 
ZuROHBRiA PARVispiNATA, 8. Buckman. Plate XLIX, figs. 18—20 ; Plate L, figs. 
1—3. 
Discoidal, compressed, imcarinate. Whorls quadrate, changing to gibbous- 
sided elliptical, at first smooth, afterwards striate, then possessing costse furnished 
with a spine at the outer end, and, lastly, having plain direct ventrally-inclined 
costag. Ventral area uncarinate, slightly arched, fairly defined during the spinous 
stage ; but afterwards narrower, more gibbous, not defined, crossed by obscure 
arcuate costse. Inner margin fairly defined, shallow, upright. Inclusion about 
one-third. Umbilicus open, ornamented with ribs bearing small spines pressed 
into the succeeding whorls ; the centre smooth. 
This species is a development of Zurcheria pugnax in a retrogressive sense. 
In its immature stage it has a quadrate-shaped whorl like pugnax" and the inner 
end of the rib is very slightly swollen — the remains of the second row of spines. 
The larger specimen, which is presumably mature, shows a complete change — the 
spines are lost, the whorls are more compressed and more elliptical. The inner- 
most whorls of the species are smooth as in pugnax ;" but they appear to remain 
smooth for a longer time. This may be due either to the larger size of the species, 
or to the modifying action of earlier inheritance. The absence of a distinct inner 
row of spines, and the slightly less pronounced ribs effectually separate this species 
from Zurcheria pugnax. 
This species is extremely rare ; the two specimens figured are all the material I 
have seen. The young specimen depicted in PI. L, figs. 1 — 3, is in my collection. 
The larger specimen I purchased from the collection of the late Dr. Wright, and 
it is a very fine example of this rare genus. 
The faint carina observable in fig. 19 and the lower part of fig. 20 is a false 
carina, due to the fact that the test of the inner part of the overlapping body- whorl, 
which must have extended another half-volution, had not been absorbed and 
amalgamated with the test of the whorl upon which it rested. This false carina^ 
therefore, is really a feature of the inner part of the succeeding, but lost, whorl. 
The Concavum-zone of Bradford Abbas, Dorset, is the horizon for the smaller 
specimen ; and there is no doubt that the larger example came from the same bed, 
as the matrix is so easily recognisable ; but it was not labelled, and, in fact, was 
enveloped in matrix when I bought it. 
