10 MOLLUSCA FROM THE GREAT OOLITE. 
different, being in JV. dispansus about one third, and in JV. excavatus about the half of 
the diameter of the shell ; the form also of the umbilical cavity varies in the two species ; in 
NV. excavatus, the sides of the cavity are regularly conical, as shown in Mr. Sowerby’s figure, 
above quoted, and in the ‘ Pal. Fran. Terrains Jurassiques,’ t. 30 ; in JV. dispansus the outer 
margin of the umbilicus is obliquely flattened, or subconical, the inner side being 
rather steep. 
A single specimen only has been found of this species in the shelly beds of the Great 
Oolite near Minchinhampton. 
Navtitus Baserrt. Plate I, figs. 1, 1a. 
N. Testa discoided, compressa, levigatd, subumbilicatd ; anfractibus angulatis, com- 
pressis ; apertura compressd subquadrata ; septis viv sinuosis ; siphunculo (?) 
A compressed, smooth shell, or only slightly marked by the lines of growth, with 
angular embracing volutions, leaving but a faint trace of an umbilical cavity ; aperture 
somewhat quadrilateral, narrowed above, and wider than it is long; the septa are slightly 
sinuous, curving towards the umbilicus and outer margin. 
This species is allied to JV. truncatus, Sow., from the Lias, but is distinguished by the 
form of the mouth, and character of the septa. 
Locality. Great Oolite near Minchinhampton. 
We have much pleasure in dedicating this species to our friend, James Baber, Esq., of 
Knightsbridge, whose interesting collection of fossil remains is always liberally opened to - 
public view. 
NaUTILUs sUBTRUNCATUS. Plate I, figs. 2, 2a. 
N. Testa discoided, inflata, levigatd, sulcatd, subimperforata ; anfractibus rotundatis 
(jun.), subangulatis (adulta) ; aperturd depressd, subquadratd ; septis (2), siphunculo (?). 
A smooth, or slightly furrowed, and somewhat inflated shell, with rounded and 
embracing volutions in the young state, which become truncate, or subquadrate, in the adult, 
and having a very shallow, or slightly impressed, umbilicus. Aperture about twice as 
wide as it is high, flattened above, and somewhat compressed laterally. 
This shell has the general form of the WV. /atidorsatus, D’Orb. ‘Terr. Jur.’ t. 24, but the 
broad umbilicus and more quadrate form of the young shell in that species readily 
distinguish them. This species belongs to the section of imperforate Nautili, of which 
NV. truncatus, Sow., N. clausus, D’Orb., are examples ; a group, the species of which were 
not apparently very numerous during the Jurassic period. 
Locality. Great Oolite near Minchinhampton. 
