294 
INFERIOR OOLITE AMMONITES. 
simply with more or less direct ventrally-inclined costge. Ventral area rounded, 
smooth, or crossed by arcuate radii Suture-line with a well-marked trifurcate 
superior lateral lobe, a superior lateral saddle deeper than the other saddles, a 
lopsided inferior lateral lobe, and an inferior lateral saddle very shallow when 
compared with the superior lateral. 
Douville thus characterised his genus : — "Ammonite of the trihe Lissoceratinse, 
with compressed, open whorls, rounded on the ventral area; the whorls orna- 
mented with slight sickle-shaped {factiliformes) ribs,^ which disappear before they 
reach the ventral area, and also with fine growth- lines parallel to the ribs, forming 
upon the ventral area a kind of rounded tongue, strongly projected forwards. 
The length of the body-chamber is a little more than half a whorl. Type, 
Z. Uhaldi." 
" This genus only contains the one species from the Bajocian of Toulon, to 
which the above description applies, and this species we dedicate to the Brother 
Ubald of Sollies-Pont." 
It is only recently, practically speaking, that any specimens of this genus 
have come under my notice ; and it is later still since any s^w species have been 
described or figured. In one respect the genus holds a unique position ; because 
it was erected to contain a single and very distinct new species, and no other 
species described up to that time bore any really close relationship to it. Since 
that time, however, various new species have been brought to light. 
The genus was founded by Douville (op. cit.) on Zurcheria Ubaldi, and about 
a year afterwards Vacek^ described as Hammatoceras two species, "jjv.gnax " and 
pertinax,'' which evidently belong here. To these I have now to add two more 
new species. 
My reading of the biological relationship of these species is as follows : — 
" Pugnax^' is the earliest form biologically, and it shows, according to Vacek's 
description, a smooth stage, and an unispinous developing into a bispinous 
stage, to which the greater part of the fossil belongs. 
" Pertinax " and the new species to be described are descendants from 
'^'pu'juax," which have retrogressed to the unispinous stage ; and the fact that 
they have lost the second row of spines is due to the law that in retrogression the 
latest acquired characters are lost first. That these species also show a somewhat 
1 Douville distinguished scythe-shaped {falciformes) aud sickle-shaped {facidiformes) ribs. The 
Latin word, falx, folds, means both sickle aud scythe, aud the word falciform is usually in thi.? 
country applied to true sickle-shaped ribs (example, Harpoceras falciferuin), though the scythe- 
shaped ribs of some of t\\Q. Arietidas are also often called "falciform." I have found it necessary 
to adopt a more precise nomenclature for the various forms of ribbing, and have confined the term 
" falciform " to the true sickle-sliaped ribs. 
2 " Ool. Cap San Vigilio," ' Abb. k. k. geol. Eeichsanstalt,' Bd. xii. 
