176 BRITISH SILURIAN BRACHIOPODA. 
impossible to know where to draw a definite line of demarcation among these many 
varieties, or rather modifications in shape, of this single most variable species. In some 
specimens the transverse striz are finer and closer than in other examples; while in 
some specimens of the variety diodonta, these last, such as in fig. 23, are wide apart, 
prominent, or scale-like. I am not, however, certain whether 7! é¢dentata of Dalman 
(not of Sowerby) may be a distinct species or not, and therefore I must leave this an 
open question. 
The next point to determine is the name the shell should retain, for some confusion 
and uncertainty seems to have prevailed upon the subject. In 1767 Linné briefly 
described his Anomia plicatella, but gave no reference to figures, and consequently it was 
not possible to be certain what was the shell intended for that species, and a Spirifer was 
subsequently by some paleontologists, myself included, rightly or wrongly referred to the 
Linnean species. In 1821 (at p. 67 of the 8th vol. of the ‘Nova Acta Soc. Upsa- 
liensis’) Wahlenberg described a 2hynchonella by the designation of Anomites plicatella, 
and referred for its figure to Linnzeus’s ‘Mus. Tessinianum,’ p. 88, pl. v, fig. 5; but 
Wahlenberg seems to have overlooked the fact that Linné had himself, in the 12th ed. of 
his ‘Systema Nature,’ referred that figure to his Anomia reticularis ; and in Turton’s 
translation of the last-named work (vol. iv, p. 282, 1802) the same reference is so repro- 
duced. It is quite possible, and even probable, that in giving that reference of figure to 
A. reticularis, Linné committed a mistake, and some naturalists have even considered 
the Linnean 4. /acunosa to be referable to the species under description, whilst others 
have applied that name to the shell now known as RA. Wilsoni. We therefore have no 
positive evidence that the species here described by the name of Rh. borealis was the 
Anomia plicatella of Linneus. 
In September, 1825, James Sowerby, in his ‘ Mineral Conchology’ (vol. v, p. 167, 
pl. 508, fig. 1), correctly described and illustrated a large Jurassic R/ynchonella, 
under the designation of plicatella, which name will have to be preserved; and 
consequently, whatever subsequent naturalists may have supposed to have been the 
A. plicatella of Linnzus, we cannot adopt their view, as the name had for the first time 
been given to a well-defined species by Sowerby. It is quite true that, in 1828, Dalman, 
and after him Hisinger, described and figured the shell here described under the 
designation of 7. plicatella ; but that name cannot, as I have said, claim precedence over 
that of Sowerby. At page 67 of his ‘ Ueber Terebrateln,’ Von Buch describes a Silurian 
shell under the designation of Zerebratula borealis, Schlotheim, and refers us for a figure 
to Schlotheim’s ‘Nachtrage,’ 1, pl. xx, fig. 6 (there erroneously named Z. Jacunosa), 
and since then Bronn and several other paleeontologists have adopted the term dorealis 
for the shell under description ; and this name I think should be retained, as it puts an 
end to the confusion created by the uncertainty relating to Linneeus’s species. I may 
here mention that the name dorea/is was first published in the catalogue of Schlotheim’s 
collection, and without any further reference (in 1822), and would have remained simply a 
