10 MOLLUSCA FROM THE GREAT OOLITE. 



different, being in N. dispansus about one third, and in N. excavatus about the half of 

 the diameter of the shell ; the form also of the umbilical cavity varies in the two species ; in 

 N. 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 N. 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. 



NAUTILUS BABERI. Plate I, figs. 1, la. 



N. Testa discoided, compressd, l&vigatd, subumbilicatd ; anfractibus angulatis, com- 

 pressis ; aperturd compressd subquadrata ; septis vix 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 N. 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, 2. 



N. Testa discoided, inflatd, Icevigatd, sulcatd, subimperforatd ; anfractibus rotundatm 

 (jun.), subangulatis (adulta] ; aperturd depressd, subquadratd ; septis (?), 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 N. latidorsatus, 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 

 N. 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. 



