RoPER^ on Biddulphia. 
21 
Zygoceros stiliger aud Z. bipons, Elir. Ber. Pro., 1844, p. 273, Ber- 
muda, are considered doubtful forms, both by Ehreuberg and Pro- 
fessor Bailey. Prom an examination of many specimens, I consider 
they should be united with the Hemiaulus of Ehrenberg. 
Zygoceros surirella. Ehr. Ber. Trans., 1840, t. vi, f. 12. Probabl.)» 
allied to the forms figured as Denticula, by Professor Gregory, in 
his 'Memoir on the Diatoms of the Clyde/ tab. ii. 
Zygoceros navicula. Ehr. Microg., t. xix, f. 22. Probably an an- 
nulus of Bhabdonema. 
The following are species described from small fragments 
erroneously referred to tlie genus^ or altogether unknown to 
me : 
Bid. ursina. Ehr. Ber. Pro., 1844, p. 200 • 1 t> ^- f i 
-o -ni T\/r- ^ i .. „ Parts 01 valves 
i5ID. URSINA. MM. i5er. rro., iS^fc^, p. ^^DU • 1 T> ^- e 1 
-o -ni T\/r- ^ i .. „ Parts 01 valve; 
Bid. gigas. Ehr. Microg., t. xxxm, xn, i. 11 . ). , i 
Denticella eragillaria. Ehr. Ber. Proc, 1844, p. 79 J 
1 The 
eneric 
P- 
Odontella amphicephala. Ehr.Ber.Proc.,1845,p.363 
Zygoceros siculus. Ehr. Micros:., t. xxii, f. 53 . , •, . 
Zygoceros paradoxa. Ibid., f. 54 . ,\ Position quite 
Zygoceros circinnus. Baik?y, Notes, t. i, f. 19, 20 .J ^^^^^^^own. 
Bid. ? BREVis. Ehr. Ber. Proc, 1845, p. 361. • 1 tt i 
Bid. cirrhus. Pritch. Inf., p. 457 . . / ^^^^^^^o^^- 
Before concluding^ I propose to offer a few remarks on 
tlie affinities of the genus^ and the forms that should be 
grouped in proximity with it^ in any natural arrangement of 
the class. I have already stated my reasons for placing the 
Eupodiscus radiatus of Smith in the present genus_, which he 
had included as a free form in his first sub-tribe ; but I should 
also propose to place the whole genus Triceratium^ included 
by him under the same head^ as an intermediate connecting 
link between Amphitetras and Eiddulphia^ to which_, in the 
structure of the frustules^ they nearly approach^ and then 
together y/ith Isthmia^ and perhaps the five- angled Amphi- 
pentas of Ehrenberg^ we should form a group most closely 
allied_, both in habit and growth. This arrangement has already 
had its advocates to a certain extent_, as Kiitzing places his 
families of Biddulphise and Angulatse in juxtaposition ; and 
Meneghini states^^ that according to him^ the former group 
has affinity with none but the following one (Angulatse), 
and^ in a letter he had received from Kiitzing^ he intimated 
his thoughts of reuniting them with the Tripodisceee (Eupo- 
discus^ Smith). Mr. Brightwell^ also^ in his paper on Trice- 
ratium^ remarks^t " that looking at Triceratium favus as the 
most perfect plan on which this group is constructed^, we 
find all the species diverging from it^ and carrying us to 
analogous forms in other groups ; and further, that placing 
* Eay Soc , 1853, p. 486. 
-f- ' Mic. Journ.,' vol. i, p. 252. 
