346 
THE TANGANYIKA PROBLEM. 
Tanganyika form and that of the old Jurassic deposits. 
Among the marine oolite there is a type of shell which is 
closely similar to, but quite distinct from, Purpurina bcllona , 
and which has received the name Purpurina inflata. 
Hudleston, in his monograph on the Jurassic gastropods, 
did not separate these two forms from one another, but he 
figured the types, of which the two shells are characteristic, 
upon different plates. It has long been a moot point 
among conchologists whether Smith’s genus, Paramelania , 
was really distinct from Woodward’s Nassopsis, and when 
we compare the two forms of Purpurina , to which I have 
just referred, with the two living Tanganyika types, we 
find that, not only is Purpurina bellona conchologically 
indistinguishable from Paramelania damoni, but also that 
Purpurina inflata corresponds equally closely with Nassopsis 
nassa (see Figs, on p. 347, upper and lower). 
In the same marine Jurassic series of gastropods there is 
another characteristic type of shell which has been grouped 
together under the generic name Amberleya. The genus 
was originally formed by Morris and Lycett, but was sub- 
sequently modified by Hudleston, and, as amended by him, 
the generic diagnosis runs as follows: — “Shell turbinate, 
more rarely trochoid, rather thin, imperforate or nearly so ; 
sub-elongate, frequently turreted ; sutural space wide ; 
ornamented with spiral bands, usually spinulous or nodular, 
some of which are prominent. The interspaces are finely 
striated, the strise being slightly oblique to the axis. 
Sometimes these fine lines are strong enough to represent 
fine axial ribs. Base rounded, spirally ribbed and marked 
by fine radial strise ; aperture sub-oval, but varying 
according to age, in the adult more or less rounded, so as 
to become sub-oval or sub-circular ; there is usually a con- 
siderable deposit of callus ; outer lip thin, often crenulate.” 
