48 
GrevillE; on the genus Auliscus. 
it from all others. The radiating costse are all slender and 
somewhat faint; those passing from the -ambilicus to the 
processes widely converging ; some of the lateral ones rough 
for a short distance from the margin, with very minute api- 
culi. Umbilicus rather indistinct. Processes generally very 
large^ not truly circular^ but often tending to a very obtusely 
triangular figure^ sometimes very broadly ovate. 
Radiating lines punctate or scabrous. Valve strictly 
circular (except in A. punctatus, which is nearly so). 
Auliscus pruinosus, Bail. — Valve circular^ with a large, 
smooth umbilicus ; radiating lines all minutely scabrous_, be- 
coming close and numerous towards the margin. Diameter 
•0055". (Fig. 13.) 
Auliscus pruinosus, Bail. — *^ Notes on New Sp. of Mic. 
Organ.^ Smithson. Contrib./ vol. vii), p. 5, figs. 5 — 8. 
Balfs, in Pritch. Inf., 1861, p. 845. (PL vi, fig. 1.) (Bad.) 
Hah. In estuaries, &c., from Massachusetts to the Gulf 
of Mexico ; Prof. Bailey. At Black Rock, Long Island ; 
Dr. Lewis. Var. with three processes in Savannah River 
mud; Dr. Lewis. Georgia; F. Kitton, Esq. 
A most charming diatom, scarcely to be recognised by the 
published figures. In none of the specimens which I have 
seen is there any trace of the bevelled edge described by 
Professor Bailey, and which in his figure has the appearance 
of a broad border. Nor are the processes so very remote 
from the margin; but tins I apprehend to be a variable 
character in several of the species. The most graphic idea 
I can give of the general appearance of the valve, arising 
from the numerous plumose, rough lines, is that conveyed by 
the term frosted — a disc of the most exquisite and sym- 
metrical frost-work. The umbilicus is a clear, circular, blank 
space, from which the lines radiate, at first rather widely, 
but soon approximating from the addition of intermediate 
lines, like the lamellae in many Agarici, become fine and 
extremely numerous as they approach the margin. When 
closely examined they are seen not to be punctate, but 
rather resemble delicate scratches on glass, the roughness 
of the edges causing the frosted appearance. The processes 
are large and handsome, with a broad border. I have availed 
myself of Mr. Kitton^s kindness, and given a representation 
of the three-process variety from a splendid example in his 
cabinet. 
Auliscus radiatus, Bail. ? — Valve circular, with obsolete um- 
bilicus, and striated marginal border ; lines all regularly and 
conspicuously punctate, those converging to the processes 
