Greville^ on New Diatoms, 
125 
cess of the other. Such an arrangement exhibits a remark- 
able analogy with that which exists in Syndetocystis, a MS. 
genus^ to be described by Mr. Ralfs in his forthcoming 
supplement to the Diatomacea; of Pritchard^s ^ History of 
Infusoria/ It was discovered in the Barbadoes deposit^ and 
also belongs to the Biddulphia family. In that most wonderful 
genus the valves are nearly circular, fringed with cilise, and 
furnished with two intra-marginal rounded processes, and in 
the centre with another solitary process, erect, cylindrical, 
and elongated, and terminated by a laterally projecting ring. 
Looking at frustules in situ, in the front view, it is perceived 
that the stalk of the process of one valve passes through the 
ring of the process of the opposing valve, and, as this is the 
mutual position, the two frustules move freely as on pistons, 
and can be pulled asunder until the respective rings are 
brought into contact, but, of course, no further. Nothing 
but force can separate them. In the cabinet of my friend 
Mr. George Norman is a chain of four frustules so united. 
Rutilaria elliptica, Grev.^ — Valve narrow-elliptical, raised 
at the angles into two short conical elevations. (Figs. 9, 
10.) 
Rutilaria elliptica, Grev.- — ' Journ. of Mic. Sci.,^ Vol. Ill, 
New Series, p. 229, PL IX, fig. 3 (valve). 
The figures which I am now able to offer will, it is hoped, 
render the structure quite intelligible. The front view ex- 
hibits four valves in situ, with the intermediate zone. The 
figure of the valve I formerly published was simply a side 
view. I now give the valve as seen under the most favorable 
circumstances for illustrating its relation to Biddulphia, viz., 
a partially front view. 
Rutilaria superba, n. sp., Grev. — Large ; valve elongated, 
oblong in the middle, gradually contracting towards each 
end into a narrow neck, which again dilates, and then 
suddenly terminates in a broadly elliptical, subacute apex. 
Length -0065". (Figs. 11, 12.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. 
A fine species, with frustules almost as long as R. epsilon, 
but with a totally different diagnosis. The species to which 
it comes nearest is jR. ventricosa ; but it differs (so far as we 
know at present) in its far more elongated form and in the 
dilated ends of the valve. I have seen many specimens of 
R. ventricosa, none of which exhibit the last-named character; 
on the contrary, the prolonged extremities of the valve are 
sometimes more slender and attenuated than they appear 
in my figure (^iMic. Journ.,' Vol. Ill, N. S., PL IX, 
