(3) ‘The shells of our native species of _Pupa_, _Clausilia_, and _Bulimus_ (with the exception of _Bulimus detritus_) show but faint annual markings. They can hardly require more than two years for their complete development. The great number of living individuals with full-sized shells belonging to these genera, as compared with the number which possess smaller shells, makes it probable that these animals live in the mature condition longer than our other _Helicidae_. I have always found full-sized shells present in at least two-thirds of the individuals of these genera characterized by much-coiled shells—a proportion which I have never seen among our larger _Helicidae_. Nevertheless direct observations as to the length of life in the mature condition are still wanting.’ (4) ‘The _Helicidae_ live from two to four years; _Helix sericea_, _H. hispida_, two to three years; _H. hortensis_, _H. nemoralis_, _H. arbustorum_, as a rule three years; _H. pomatia_ four years. Fertilization is not in these species strictly confined to any one time of year, but in the case of old animals takes place in the spring, as soon as the winter sleep is over; while in the two-year-old animals it also happens later in the summer.’ (5) ‘The _Hyalineae_ are mostly biennial: they seldom live three years, and even in the largest species such an age is probably exceptional. The smallest _Hyalineae_ and _Helicidae_ live at most two years. The length of life is dependent upon the time at which the parents are fertilized, for this decides whether the young begin to shift for themselves early in the summer or later in the autumn, and so whether the first year’s growth is large or small.’ (6) ‘The species of _Limnaeus_, _Planorbis_, and _Ancylus_ live two to three years, that is they take two to three years to attain the full size. _L. auricularis_ is mostly biennial, _L. palustris_ and _L. pereger_ two to three years: I have found that the latter, in the mountains at Oberstorf in the Bavarian Alps, may exceptionally attain the age of four years, that is, it may possess three clearly defined annual markings, whilst the specimens from the plain never showed more than two.’ (7) ‘The _Paludinidae_ attain an age of three or four years.’ (8) ‘The smaller bivalves, _Pisidium_ and _Cyclas_, do not often live for more than two years: the larger _Najadae_, on the other hand, often live for more than ten years, and indeed they are not full grown until they possess ten to fourteen annual markings. It is possible that habitat may have great influence upon the length of life in this order.’ ‘_Unio_ and _Anodonta_ become sexually mature in the third to the fifth year.’