The first known members of the land Pulmonata (_Pupa_ [?], _Hyalinia_) are from the Carboniferous of North America. Similar but new forms appear in the Cretaceous, from which time to the present we have an unbroken series. The characteristically modern forms, according to Simroth,[31] are Helices with thick shells. According to the same author, _Vitrina_ and _Hyalinia_ are ancestral types, which give origin not only to many modern genera with shells, but to many shell-less genera also, _e.g._ _Testacella_ is probably derived through _Daudebardia_ from _Hyalinia_, while from _Vitrina_ came _Limax_ and _Amalia_. A consideration of the radulae of the genera concerned certainly tends in favour of these views. Godwin-Austen, speaking generally, considers[32] genera of land Pulmonata with strongly developed mantle-lobes and rudimentary shell as more advanced in development than genera in which the shell is large and covers all or nearly all the animal. CHAPTER II LAND AND FRESH-WATER MOLLUSCA, THEIR HABITS AND GENERAL ECONOMY The majority of the Land Mollusca are probably more sensitive than is usually believed. The humidity of the air must affect the surface of their skin to a considerable extent. Every one has noticed how the snails ‘come out’ on a damp evening, especially after rain. As a rule, they wait till rain is over, probably objecting to the patter of the drops upon their delicate tentacles. Snails kept in captivity under a bell-glass are acutely sensitive of a damp atmosphere, and will bestir themselves after rain just as if they were in the open air. Certain Helices which are accustomed to live in moist places, will find their way to water, if removed from their usual haunts. A case is recorded[33] of a specimen of _H. arbustorum_, kept in a kitchen, which used to find its way directly under the cold water tap, and appeared to enjoy the luxury of a douche. How delicately the conditions of life are balanced in some of these creatures is seen in the case of _Omalonyx_, a genus akin to _Succinea_, which is found in Brazil and the northern parts of South America. It lives creeping on plants which overhang the margin of water, but perishes equally, if placed in the water itself, or removed to a distance from it for any length of time.[34] =Endurance of Heat and Cold.=--The Mollusca are capable, at least as far as some species are concerned, of enduring severe extremes both of cold and heat. The most northern pulmonate yet observed is a fresh-water species, _Physa_ (_Aplecta_) _hypnorum_ L. This hardy mollusc, whose shell is so fragile as to need most careful handling, has been noticed on the peninsula of Taimyr, North Siberia, in 73° 30’ N. lat, a region whose mean annual temperature is below 10° F. with a range of from 40° F. in July to -30° F. in January.