RoPER^ on Biddulphia. 
9 
Denticella TiiiDENTATA. Ehr. Ber. Pro., 1844, p. 79. 
Biddulphia tiudens. Pritcli. Inf., 1852, p. 457; Ehr. Microg., 
1856, t. XX, f. 53, I. xix, f. 21. 
Denticella simplex. Shadbolt, Mic. Jour., 1854, t. i, f. 16. 
Denticella margaritifera Ibid., t. i, f. 17. 
Biddulphia tridentata. Elir. Microg., 1856, t. xviii, f. 52, t. xxi, 
f. 24. 
Denticella polymera. Ehr. Ber. Pro., 1844, p. 266 ; Bailey, Sil. 
Jour., 1845, t. iv, f. 20 ; Pritch. Inf., 1852, p. 845. 
Odontella polymera. Kiitz. Spec. Alg., 1844, p. 137. 
This fine and well-marked form has been found always 
with the same peculiar characters in so many localities^ that 
there can be little doubt it is entitled to rank as a distinct 
species ; as far as I am aware, it has not yet been met with 
on the coasts of England, though in some respects it ap- 
proaches the preceding species, B. regina, of the ' Synopsis.^ 
Through the kindness of Professor Williamson, I have been 
able to examine authentic specimens of that species, of which 
the figure in Professor Smith's volume gives a very correct 
representation. It differs from the form described by 
Professor Bailey as Tiygoceros Tuomeyii, in having all the 
lobes and processes of nearly equal length, in the absence of 
the spines on the summits of the lobes, in the greater depth 
of the constrictions, and in the greater size and more irregular 
arrangement of the granular markings or reticulations. In 
B. Tuomeyii, the processes are long, narrow, and usually 
twice the length of the adjacent, and about one third longer 
than the central lobe ; all the median elevations are spinous, 
and always more widely separated than in B. regina. As I have 
found these peculiarities constant in specimens from various 
localities, as well as in the figures in Ehrenberg and 
elsewhere, they appear to afibrd sufficient ground for specific 
distinction. 
In describing this species. Professor Bailey states, that at 
the base of each of the swellings, the shell often shows 
perforations, and the whole surface is covered with shagreen- 
like asperities/''^ these markings at the base of the lobes 
are not perforations, but appear to arise from slight de- 
pressions, which are brought more prominently into view, 
from the greater projection of the valve at these points than 
at the base of the constrictions ; the same appearance is seen 
in B. regina. (See ^ Syn.,' t. xlvi, fig. 3.23.) 
In examining the synonymy of this species, Ehrenberg's 
name of Denticella tridens appears to have the priority as to 
date, but as it occurs not unfrequently with only one lobe. 
* 'Siliman's Journal,' 1st series, vol. xlvi, p. 138. 
