MR. H. B. BRADY ON THE RHIZOPODAL FAUNA OF THE SHETLANDS. 465 
one central typical form ; the more extensive the series of specimens examined, the more 
closely connected the links of the chain which binds the whole series, and very fre- 
quently it is impossible to say with certainty under what particular name specimens of 
the intermediate forms should stand. At the same time these subspecific and varietal 
distinctions are of considerable importance to the zoologist and the geologist as indicating 
the existence of certain climatal and bathymetrical conditions, and are in practice equally 
necessary whether representing true species or not. The varietal forms are sufficiently 
recognizable and sufficiently characteristie of habitat to deserve binomial appellation, 
and, so long as the connexion is understood, it is unnecessary to overload the terminology 
by constant repetition of the specific name as well. Whilst preserving, therefore, the 
specific names hitherto adopted, they have been arranged under their respective types in 
order to preserve the connexion indicated. Subvarietal names have only been employed 
in a few cases in which no author has thought the distinction sufficient to merit specific 
appellation. The names used in Professor Williamson’s Monograph have been given in a 
parallel column, together with reference to his figure of each form. 
Of the species figured by Professor Williamson only ten will be missed in the Table of 
the Shetland forms, and it seems probable that one or two, at least, of these have been 
introduced on the authority of chance fossil specimens washed out of the strata on the 
sea-coast. Such errors are frequent in the works of Walker and Boys, and some other 
conchologists, and are corrected with difficulty. The two species of Frondicularia figured 
in the Monograph (pl. 2. figs. 50 & 51), from specimens found at Sandwich, have pro- 
bably been derived in this way from the chalk cliffs of Kent. Many species of the genus 
are common in the chalk, and amongst them the particular forms alluded to, but are 
almost unknown in a recent state in the seas of temperate regions. In the same way 
Cristellaria subarcuatula, var. costata, pl. 2. fig. 63 (Marginulina raphanus, d'Orb.), and 
C. subarcuatula, var. costata, pl. 2. figs. 64 & 67 (Planularia strigilata, Reuss), are 
probably derived, the former from the Tertiary beds near Sandwich, the latter from the 
Oxford or the Kimmeridge clay of Dorsetshire. With reference to another species, 
P eneroplis planatus, one or two specimens of which were supposed to have been found 
in Shetland sand, I have the following memorandum from Mr. Jeffreys, which renders it 
necessary to exclude it from the British list; and as Vertebralina striata was found in the 
same parcel, it must share the same fate. Mr. Jeffreys writes :—“ I have reason to believe 
that the admission of Peneroplis planatus into the list of British Foraminifera — 
dental and erroneous, so far as I was concerned. Soon after my return from a scientific 
excursion to the coast of Piedmont, Mr. Barlee sent me some shell-sand which he had 
dredged in Shetland, and I used for the separation and examination of it the same sieves 
that I had with me in Italy. Although these sieves had been carefully washed and 
cleaned before 1 left Genoa, a few remnants of my Mediterranean dredgings may have 
been left in the folds of the wire-work within the rim, and hence the mixture of Southern 
and Northern productions." Peneroplis is common in the Mediterranean, as is also 
Vertebralina ; and as this is the only recorded instance of their occurrence in so high a 
latitude, it has probably come about accidentally as above suggested. usd 
~ In completing the list of Shetland Foraminifera, I have inserted the names of four or 
