46 
THE LOWER LIAS OF KEYNSHAM. 
Am. {Microderoceras) planicosta^ Sow. This, the earliest 
of the capricorn ammonites, is characterized by simple ribs, 
continuous across the sides and rim ; in their passage across 
the rim, they broaden out and become quite flat topped. 
(According to Dr. Brauns, this flattening is peculiar only 
to whorls that are covered by later ones, and is due to an 
absorption of the shell). 
Am. {Oxynoticeras). A fragment, showing a partially open 
umbilicus, is the only evidence we have yet found of this genus. 
Nautilus. — The only specimens we have found occur in 
the Arietes zone ; large nautili are especially common at the 
top of the Bisulcatus Beds. 
N. intermedius., Sow. Following Dr. Brauns, we have 
grouped the large nautili under this specific name since they 
exhibit the following characters : 
Umbilicus partially open, siphuncle above the centre, shell 
marked with strong longitudinal striae, aperture flat topped, 
and taller than broad. (We are inclined to think that 
N. striatus is merely the young form, in which the aperture 
is rounded ; at least we have never seen from the Lower 
Lias a full-grown nautilus, which is not more or less late- 
rally compressed and flat rimmed.) 
Gastropods. 
A long list of species could be compiled from the rich beds 
of the Calcicosta series, but, since the majority of the forms 
have already been described by Charles Moore in the paper 
already alluded to, we merely append the names of a few of 
the commonest species. (The naming is partly from the 
works of Terquem, Terquem and Piette, and Dumortier, but 
chiefly from the excellent figures in Tate and Blake’s York- 
shire Lias.) 
Pleurotomaria anglica^ Sow. ( — PI. similis, 0pp.) 
PI. basilica^ Oh. and Dew. 
