136 EEPOiiT— 1872. 



subniei'pfed, aud they coustitute a continuous line of commuuicatiou hj water be- 

 tween the lower and upper stream, however great the difterence in level may be, 

 a higher fall merely requiring a greater number of locks than a lower. To mo- 

 derate the velocit}' of the flow of water through the trough-aperture, the apertures 

 are not placed in continuous line, but diagonally opposite, with small jetties. The 

 difference in level between each lock will generally be about 15 inches, and tho 

 size of the locks G or 7 feet square ; the area of the trough-apertures about 1 foot, 

 that of the feed-apertures being about one fourth larger. When space is limited 

 and the height to be surmounted considerable, the locks may be arranged like a 

 winding or spiral stair. The plan of construction ia not costly ; generally it may 

 be made of timber. ^ 



Mr. II. E. Deesseb exhibited British Specimens of Jlijpohis ichrina, 



Sur les Bents du Macrauchcnia et leur Mode de Remplacement. 

 Par M. Paul Gekvais. 



Le Prof. Paul Gervais rappelle d'abord les caracteres sp^ciaux de la fauue qua- 

 ternaire propre a I'Amerique meridionale, et les principaux travaux dont elle a ete 

 I'objet dans ces deruiers temps. Le nouveau memoire qu'il se propose de consacrer 

 aux animaux propres a cetto fauue paraitra parmi ceux de la Societe Geologiquo 

 de France, et comprendra des details relatifs a plusieurs des especes ^teintes de- 

 couvertes dans I'Ann^rique du sud, particalieremcnt au Macrauc/ienia. 



M. Paul Gervais fait connaitre en partie la premiere dentition de ce genre si 

 curieux de raammiferes, et il en decrit en meme temps les dents de remplacement 

 pour la machoire inferieure. Oelles de ces dents qui rdpoudent aux incisives, aux 

 canines, et aux avaut-molaires sout remarquab'cs par la disposition festonnee de 

 leur couronne, qui rappelle d'une maniere inatteudue la forme caracteristique de 

 Vlf/iianocJon. M. P. Gervais prdsente une planche sur laqucUe ces caracteres sont 

 representes. 



En ce qui concerue la classification du Maci-auchcnia, il -ponse, axecM. Owen, 

 que cet animal doit etre rapprocht? de Ehinoceros, et qu'il appartient a la meme 

 famille que ces derniers ; ce qui lui parait resulter de I'ensemble des caracteres pro- 

 pres a ce genre qui repete dans la st?rie de Junientes, on Anisodactyles, une condition 

 comparable a celle des Anoplotheriums parmi les I'orcins, et foiiruit, parmi les 

 Rhiuocerides, I'examplc d'une formule dentaire ramenee a son expression typique. 



Les nouvelles etudes de M. P. Gervais complcteront a certains egards les notions 

 publiees par MM. R. Owen, Bravard, et Bunneister, ainsi que par lui-meme, rela- 

 tivement a ce genre singulier de Mammiferes. Les pieces qu'il a examinees font 

 partie des acquisitions lecemnient accomplies par le Museum de Paris. 



Diversity of Evolution under one set of External Conditions. 

 By the Eev. Jonx T. Gvlick. 



Note on the cmjyloyrnent of Yachts in Deep-sea liesearches. 

 By Capt. Maeshall Hall, F.G.S., F.C.S., cj-c. 



Having had some experience in dredging &c. from a yacht, and having met 

 ■with sundry yacht-owners who would like to join in such pursuits, the author sug- 

 gests that the British Association would be a proper body to form a Committee to 

 encourage, oi'ganize, direct, and inform yachting naturalists with regard to the 

 mode in which they could be of most use. He considers that though no single 

 small vessel without steam aud experienced men could investigate a locality 

 thoroughly, yet, by an interchange of apparatus and a division of the work to be 

 done (one yacht taking current observations and sounding, another the dredging, 

 and so forth), a small squadron making a rendezvous, say, at some little-known "V\''est- 

 India island or the Canaries, might accomplish verj' complete and interesting in- 

 vestigations, besides doing valuable work nearer home. 



