2 
Greville, on New Diatoms. 
Hah. Barbadoes deposit^ Cambridge estate ; in slides com- 
municated by C. Johnson^ Esq. ; exceedingly rare. 
I regret to say that no perfectly entire valves of this 
species have been obtained ; but the only deficient part is the 
striation of the inflated portion of the valve. The sutural 
ends of the striae are, however, quite evident, and there can 
be no reason to conclude that they differ jfrom those of the 
narrower portion. In form it is allied to P. lyratum. In 
structure it varies from the other members of the genus, 
having, in addition to a groundwork of exceedingly delicate 
decussating rows of dots, a series of transverse pervious 
strise. Fine illumination and careful adjustment is required 
to bring out the characters. 
Mastogonia. 
Mastogonia Actinoptychus. (Fig. 4.) Ehr., ^Bericht. d. 
Berl. Akad.,' 1844, p. 269; ' Mikrog.,' pi. xviii, fig. 19. Kiitz., 
'Sp. Alg.,' p. 25. Ralfs, ^inPritch. Infus.,' p. 814, pi. v, fig. 59. 
As the figure published by Ehrenberg is not quite satis- 
factory, I have been induced to offer one taken from a fine 
example in my friend Mr. L. Hardman^s cabinet. The 
station given by Ehrenberg is Virginia. Mr. Hardman ob- 
tained his specimens from the celebrated Monterey deposit in 
California. They exhibit a minutely punctate structure, and 
a very variable number of radiating lines or segments. 
Ehrenberg fixes them at 13, but his own figure has 19. The 
valve I have copied shows 25, and I have seen another with 
as many as 30. It is evident, therefore, that number in this 
case is not a trustworthy character. 
Xanthiopyxis. 
Xanthiopyxis? umbonatus, n. sp., Grev. — Disciforme, cir- 
cular, broadly umbonate, the umbonate portion more or less 
covered with strong short setse. Diameter about -0040''. 
(Fig. 5.) 
Hab. Monterey deposit ; cabinet of L. Hardman, Esq. ; 
R. K. G. 
Of this fine diatom, which is by no means rare in the 
Monterey deposit, I have seen no specimen with the valves 
in situ, and I am consequently by no means certain that it 
is a genuine Xanthiopyxis. The curve of the umbo is vari- 
able, as well as the proportion of the disc which it occupies ; 
and the setae, although generally confined to the centre, some- 
