308 Mr. O. Thomas — Notes on Dr. W. KiikenthaVs 



Subvar. nov. — Sides blackish, back greyish ; margin of sole 

 liglit 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. empincorum 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. falla.T, Ckll., of A. hortensis^ Fer., 

 is merely a form of var. siibfusca, C. Pfr. The var. nov. 

 ulbipes 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 Avion 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. 



XLVllI. — Notes on Dr. W. KiikenthaVs Discoveries in 

 Mammalian Dentition. By Oldfield Thomas. 



The two important papers by Dr. W. Kukenthal recently 

 published f, and translated in the present number of the 

 * Annals ' J, render necessary a few words on the bearing that 

 the discoveries therein announced have on the theories of 

 tooth-dcsccnt current here and on the Continent. 



On the first and most essential question as to the origin of 

 the present Mammalian diphyodontism, i. 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 dipliyodontism was present in the earliest ]\Iammalia, 

 and has become reduced in the different orders to different 

 degrees, the lowest orders being paradoxically the most 



* 'The Conchologist; vol. i. p. ;W (1891). 

 t Anat. Anz. vi. pp. 86i) and lo'^S (1891). 

 i Suprd, pp. 279, i>8o. 



