462 THE ZOOLOGIST. 



numerous illustrations with which it is embellished make almost 

 sufficient amends for the shortcomings in the text, which may be 

 improved in a future edition. 



A Monograph of the Land and Freshwater Mollusca of the British 

 Isles. By J. W. Taylor. With the assistance of W. D. 

 Eoebuck, C. Ashford, and others. Part II., pp. G5-128. 

 With coloured frontispiece and numerous illustrations. 

 Leeds : Taylor Brothers, Sovereign Street. 1895. 



The first part of this new work on British Mollusca was 

 reviewed in the number for February last (pp. 79-80), when we 

 took occasion to commend the thorough mode of treatment 

 adopted by the author, and the excellence of the illustrations, 

 which are numerous. In Part II., now before us, we are pleased 

 to see this high standard of merit maintained. The author, 

 continuing his introductory observations, deals in this number 

 with the subjects of variation in form and size, colour and 

 markings, monstrosities, and auxiliary and protective organs. 

 Size is influenced not only by the obvious causes of the abun- 

 dance or scarcity of suitable and nutritious food, but is also in a 

 great degree dependent upon temperature and other circum- 

 stances. The researches of Semper on the phenomena of 

 growth upon which size is dependent, have shown that in 

 Limncea stagnalis, for example, the size attained by the shell is 

 capable of correlation with the temperature and amount of the 

 inhabited water, as assimilation and growth equally ceased if the 

 degree of warmth exceeded 90° F., or fell below 53° F. ; the 

 fullest vigour being enjoyed, and the largest size attained when 

 the temperature ranged between 68° F. and 77° F. The results 

 of these researches are of great interest, and are more or less 

 applicable to other species, as demonstrating some of the 

 conditions governing growth — and therefore size — in Mollusca 

 generally ; and clearly establish that the volume or amount of 

 water allowed to each mollusc is so decisive in its effect upon 

 growth, that in the space of six days, the difference in the size of 

 the shells of those in a large and those in a small body of water 

 becomes apparent ; the smaller the amount of water per indi- 

 vidual the smaller the shell, and vice versa. 



The colouring of the Mollusca, according to Mr. Taylor, 



