308 Mr. O. Thomas—WNotes on Dr. W. Kiikenthal’s 
Subvar. nov.—Sides blackish, back greyish ; margin of sole 
light brown. Yorkshire (Collinge). 
Subvar. nov.—Animal drab colour; foot deep yellow, margin 
bright orange. Guernsey (Roebuck). 
After a careful examination of a number of brown and red 
forms of A. empiricorum I am much inclined to group 
Mr. Roebuck’s var. brunneus as a subvar. of var. rufus, L. 
The variety subreticulatus, Ckll., might also be grouped as a 
subvariety of var. reticulatus, Roebuck. There can be little 
doubt but that the var. fadlav, Ckll., of A. hortensis, Fér., 
is merely a form of var. subfusca, C. Pfr. The var. nov. 
albipes lately described by Mr. Cockerell * is a very unsatis- 
factory one, being made from a single immature specimen. 
The white sole is such an unusual occurrence in A. hortensis 
that it is important; but specimens frequently show light- 
coloured soles in a young condition. 
The many perplexing forms of Arion which are at present 
engaging the attention of conchologists cannot be rightly 
assigned to this or that species from a mere examination of 
the external parts, and it is to be hoped that future collectors 
will abstain from adding useless synonyms to the list until 
they obtain a better knowledge of the anatomy. 
XLVIII.—WNotes on Dr. W. Kiikenthal’s Discoveries in 
Mammalian Dentition. By OLDFIELD ‘THOMAS. 
THE two important papers by Dr. W. Kiikenthal recently 
published}, and translated in the present number of the 
‘Annals’ $, render necessary a few words on the bearing that 
the discoveries therein announced have on the theories of 
tooth-descent current here and on the Continent. 
On the first and most essential question as to the origin of 
the present Mammalian diphyodontism, 7. e. the possession of 
two more or less complete sets of teeth, a milk and a perma- 
nent set, two conflicting views have been advocated—(1.) that 
this diphyodontism was present in the earliest Mammalia, 
and has become reduced in the different orders to different 
degrees, the lowest orders being paradoxically the most 
* ‘The Conchologist,’ vol. i. p. 83 (1891). 
t+ Anat. Anz. vi. pp. 869 and 658 (1891). 
~ 
t Supra, pp. 279, 285. 
