A HISTORY OF HERTFORDSHIRE Tring, and which is situated almost wholly upon the Cretaceous beds, and this formation being characteristic of a large portion of Hertfordshire, the species enumerated may, as far as they go, be considered as representative to a certain extent of the county generally. In many localities the chalk is overlaid by deposits belonging to the Eocene and Quaternary periods, and there is a corresponding alteration in the character of the flora. Not much is known of the Coleoptera of these districts, but they may reason- ably be expected to produce some species not to be found upon the outcrop of the Cretaceous beds. Where outliers of the Woolwich and Reading beds occupy extensive areas they effect a material change in the character of the soil, and an increased number of species of Coleoptera may be looked for, especially if the outlier be covered with woodland. Upon the chalk we have occurring a considerable number of the species peculiar to that formation, and it will be found that a very close analogy exists between the fauna of the Chiltern Hills district and that of similar districts in the counties of Kent and Surrey. The Middle Chalk which seems so specially favourable to the growth of several of our rare plants * is also apparently the special haunt of many of the rarer chalk-loving beetles. Here there always seems to be a greater variety of species, and two members of the genus Apion, A, atomarium and A. iva/toni, I have not yet noticed on any of the other divisions of the formation. Possibly other observers may find these two species less particular in this respect. The beech woods which flourish in and are such a notable feature of the chalky districts, harbour many characteristic species, principally sub- cortical ones, the beech being very little in favour with the Cryptocephali, Rhynchites and other phytophagous genera usually to be looked for in such situations. The flora of the chalk downs and uncultivated chalky pastures includes a large number of plants which are frequented by various beetles. It is unnecessary to detail them here, as the name of the food plant upon which a species has been found to occur in the county is given in each case in the catalogue with the locality. Even the cultivated fields in the chalky districts are often well adapted to produce an abundance of beetle life, growing as they do crops of sainfoin, lucerne and clover or cereal crops much overrun by charlock (Brassica sinapis), either kind of vegetation being capable of supporting many species of the weevil tribe and Halticidce, and for which there is usually abundant undisturbed shelter during winter in the close-growing turf and moss of the adjacent chalk downs and hedgerows. The aquatic Coleoptera are but poorly represented at present in the county list. This is partially due no doubt to the fact that I have not myself collected them quite so carefully as some of the other groups, but it must also be borne in mind that there are no extensive fen or bog lands within the county, so that probably further and more complete search will not very largely augment the number. Upwards of fifty of the species appearing in the catalogue are not at present known to occur further north. Many of these are chalk-fre- 1 Flora of Hertfordshire, pref. p. xiii. 84
