Reports and Proceedings — Geological Society of London. 43 



The various attempts which have been made to separate this 

 genus into subgeneric groups have not been altogether satisfactory, 

 owing to the difficulty of deciding what are the more important 

 structural features. A natural classification, as opposed to an 

 artificial one, should be based on the structural characters of the 

 head-shield ; and the variations in the form and lobation of the 

 glabella in the Lichadidge (as Beecher has remarked) indicate 

 differences in the relative development of the appendages and organs 

 of the head. The origin and application of the various proposals 

 for classification are considered, and certain synonyms and names 

 of prior application to other organisms are rejected. Next, the 

 characters of the original type-species of the various subgenera are 

 summarized. The second part of the paper contains a critical con- 

 sideration of the homologies of the furrows and lobes in the glabella 

 of the Lichadidee. Following Beecher's scheme, the anterior lateral 

 portion of the so-called median or frontal lobe is considered to 

 correspond to the antennulary or true first lobe of the glabella. 

 The so-called * first ' lateral lobes of Lichas would correspond to the 

 fused antennary and mandibular lobes, the true second and third 

 lobes of the glabella. The lateral lobes, which are usually termed 

 the ' middle ' or ' second ' lateral lobes, become homologous with 

 the fourth or first maxillary ; and the neck or occipital lobe or ring 

 falls into its right place as the second maxillary lobe. By means 

 of this principle an attempt is made to discover the principal lines 

 of modification along which the evolution of the head-shields of 

 the Lichadidee has proceeded. In the third part of the paper the 

 Lichadidge are divided into two great grouj)S : (1) that with a pair 

 of bi-composite lateral lobes to the glabella and a more or less 

 definite fourth pair of lateral lobes ; and (2) a group with a pair of 

 tri-composite lateral lobes, through the fusion of the fourth pair with 

 the bi-composite pair of the preceding group. Names are proposed 

 for each group, and also, where necessary, for the eight sections, of 

 subgeneric value, into which each group is subdivided. The paper 

 closes with a list of the British members of the family Lichadidee, to 

 show their distribution among the groups and sections. 



2. " Some Remarks on the Meteorological Conditions of the 

 Pleistocene Epoch," By Dr. Nils Ekholm, Meteorologiska Central- 

 Anstalten, Stockholm. (Communicated by Professor W. W. Watts, 

 M.A., F.G.S.) 



The opinion of the author on this subject differs in some important 

 respects from that of Mr. Harmer. He considers the subject under 

 two heads : (1) What are the meteorological conditions necessary 

 and sufficient to pi'oduce a permanent ice-sheet such as that of the 

 Great Ice Age ? (2) What will be the influence of such glaciation 

 on the meteorological conditions, especially on the cyclones and 

 anticyclones, of the ice-covered land and on its neighbourhood ? The 

 snow-line does not correspond with the mean annual isotherm of 32°, 

 for Verchojansk in Siberia is not glaciated, whereas the southern 

 point of Greenland is. The former has a Winter anticyclone, while 



