10 
Roper, on Biddulphia. 
and occasionally with ten to twelve, as shown in the Den- 
ticella polymera of ' Sil. Journal/ vol. xlviii, tab. iv, fig. 20, 
clearly only a large specimen of the present form, the de- 
signation tridens is so decidedly inapplicable, that I am in- 
duced to retain that of Tuomeyii, given by Professor Bailey. 
I have examined a large number of specimens of the Denti- 
cella simplex and D. margaritifera, of Mr. Shadbolt,"^ from 
Natal, and they are clearly identical with the present species, 
neither the number of the lobes or the spines being suffi- 
cient ground for specific distinction. The most characteristic 
figure of this species is given by Professor Williamson, in 
his paper on the " Levant Mud," in the ' Memoirs of the 
Philosophical Society of Manchester,' vol. viii, new series, 
tab. i, fig. 1 ; but, as that work is not generally accessible, I 
give a figure of a specimen from Californian guano, supplied 
me by my friend Mr. E-alfs. Mr. ShadbolVs figures in the 
^ Micros. Journ.,' vol. ii, tab. i, figs. 16, 17, are good repre- 
sentations of the smaller frustules, not unfrequent in the 
Natal gathering. 
Section II. — Valves lanceolate, elliptical, or orbicular, 
without undulating margins. 
4. Biddulphia aurita, Breb. Synopsis,' p. 49.) 
Marine or brackish water. A very common species on the 
coasts of England, and on those of Europe, Asia, Africa, and 
America. 
Syn. DiATOMA. auritum. Lyngb. Tent. Hydro. Dan., 1819, t. Ixii ; Hooker, 
B. El., 1833, p. 404. 
Odontella aumta. Ag. Consp. Crit. Diat., 1830, p. 56; Smith's 
Eng. Bot., t. 2842, f. 2; Harv. Man., 1841, p. 201; Kiitz. 
Bac., 1844, t. xxix, f. 88 ; Spec. Alg., 1849, p. 136 ; Pritch. 
Infus., 1852, p. 470. 
Biddulphia aurita. Breb. Cons, sur les Diat., 1838, p. 12 ; Ealfs, 
Ann. is at. Hist., vol. xii, 1843, t. viii, f. 4 ; Pritch. Inf., 1852, 
p. 456 ; Smith, Svn., 1856, vol. ii, t. xlv, f. 319 ; Microg. 
Diet., 1856, t. xiv; f. 9. 
Denticella aurita. Ehr. Microg., 1854, t. xxxv. A, 23, f. 7. 
Denticella gracilis. Ehr. Ber. Acad. Pro., 1840, p. 206, and "B. 
Trans., 1840, p. 12; Pritch. Inf., 1852, p. 344. 
This species, although common in most marine gather- 
ings, rarely occurs in much abundance, and, like some other 
members of the genus, is subject to very great variations in 
form even in the same locality, as may be seen, by compar- 
ing the various figures given in the ^ Synopsis^ of Professor 
Smith, whose description, together with that of Mr. Ralfs,t 
* ' Micros. Journal,' vol. ii. Transactions Micros. Soc, p. 17. 
t See 'Ann. Nat. Hist.,' vol. xii, 1843, p. 272. 
