476 Reviews — Douvilles Lamellihranchia. 



at depths below Ordnance Datum, at intervals of 200 feet. The 

 outcrop of the Bunter Pebble Becis and Lower Mottled Sandstone 

 occu{)ies an area of 240 square miles in the county, and it is from 

 these beds that most of tlie water is derived. A sketch-map of part 

 of North IS'ottinghamshire shows the underground water-level in the 

 Bunter in 1909 ; the contours of the water-table are drawn at 5 ft. 

 intervals, and the height above O.D. is given in feet. It is estimated 

 that the yieki, from the Bunter, of public wells is about fourteen 

 million gallons a day, and of private wells about seven or eight 

 million gallons. 



In ch. ii it is noted that the average rainfall responds to the 

 configuration of the county in a sti'iking manner. The lowest rainfall, 

 less than 25 inches, is confined to the low ground of the Trent Valley, 

 and the isnhyetal line of 25 inches coincides roughly with the 

 contour-line of 150 feet of elevation in the south and that of 100 feet 

 in the north. The isohyetal of 30 inches keeps near the contour of 

 500 feet in the west of the county. The local description of the 

 water supply is dealt with under five districts, which are partly 

 topographical and partly geological, and references are here given to 

 the fuller geological and other details contained in the subsequent 

 chapters, in which the records of well-sections and a large 

 number of analyses are brought together. 



III. — Classification des Lamellibranches, Par H. Douville. 

 Bulletin Societe Geologique de France, ser. iv, tom. xii, 

 pp. 419-67, figs. 



fl^HIS paper, owing to its publication in a journal not open to all, 

 j[ runs the risk of not receiving the attention it deserves. 



After summarizing the various systems of classification that have 

 been proposed for the Pelecypoda, beginning with that advanced by 

 Neumayr in 1883, the author discusses the nature and development 

 of the shell and roughly divides the group into those that live free, 

 those that are attached, and tlie crypt dwellers or burrowers. 



Three types of characters attach to the Pelecypoda. 



1. Evolutiovary characters. Thus in the ancient forms the shells 

 were nacreous, but became porcelainous in their descendants during 

 the course of their evolution. 



2. Adaptive characters due to environmental conditions and giving 

 rise to like forms of test in animals of distinct stocks, e.g. Mytiliis 

 and Dreissensia, Ostrea and Chondrodonta, Solen and Ensis, etc. 



3. Static characters, or those which change least. The hinge is 

 the best example of this type and is consequently the one mainly 

 relied on by the author for the purposes of classificution. 



An extremely interesting and well-illustrated section follows, giving 

 the different forms of hinge and their evolution, whilst the paper 

 concludes with a tabular statement of the phylogenetic grouping 

 proposed. 



This shows the primitive nacreous forms divided into three groups; 

 Taxodonta, comprising the free forms; Dysodonta, or fixed forms; 

 and Desmodonta, or crypt dwellers and burrowers, including such 



