INTRODUCTION. 



XXlll 



of the species resemble each other closely in appearance, both as to casque and plumage ; but 

 the fifth has a perfectly white casque and a conspicuous superciliary stripe, not observed in the 

 others. The seventh genus is Cranorrhinus, with four species, distinguished by high, upright, 

 keel-shaped casques extending half the length of the bill, with several undulations on the sides ; 

 and this genus is followed by Penelopides with three species, of much smaller size, lower 

 casques, and grooved bills. The birds of the last three genera, although they do not follow each 

 other in regular order, unknown forms being required to supply the void between each two 

 genera, still are closely related, and seem to constitute a natural group in the family. I now come 

 to birds also possessing high and largely developed casques, but which are natives of a different 

 zoogeographical region, and, as might be supposed, are rather widely separated from the members 

 of the previous genera, yet at the same time possess characters in common with them. Several 

 links are needed here to complete the line between the last-named genus and Ceratogymna, 

 the one I now reach. This has but a single species, though one that is very remarkable for the 

 form of its casque, which is large, bulky, extending over half the maxilla, rather flattened on its 

 anterior face, which is upright ; large irregular grooves also run along the sides of the casque 

 near the maxilla. Allied to this is the single species of the genus Sphagolobus, but with a 

 casque differently shaped and even larger than the other. Following this I place the genus 

 Limonophaltjs with a single species, succeeded by Bycanistes with six species, having, as a 

 rule, a casque longer than the bill, pointed anteriorly, and curving to the culmen. Next is the 

 genus Pholidophaltjs with three species without a casque, but with a roughened casque-like 

 protuberance covering the basal third of the culmen. These last five genera with their species 

 form a well-marked group, with similarly coloured plumage ; but, like the others, the links are 

 wanting by which the existing species could be more readily arranged. Through the species of 

 the last genus we are led to those birds which have bills devoid of casques, or else the latter 

 represented by flattened protuberances having the appearance of bony scales. These are contained 

 in the genus Rhytidoceros, and consist of four species, one of which, like the members of the 

 last genus, has transverse grooves at base of bill. The species of the fourteenth genus do not 

 possess casques ; but, in lieu of this appendage, the culmen is compressed laterally, and elevated 

 into a low crest descending gradually forward to the culmen. There are five species included in 

 this genus (Anorrhinus), all having long loose crests on the head and occiput. Aceros, the next 

 genus, contains but one though a large and fine species, without casque, the culmen swollen at 

 the base of maxilla. With this bird the list of the large Hornbills is finished, those that remain 

 decreasing in size until we arrive at the last one, no larger than a Jay. Exarhata, which is 

 the sole species of the genus Hydroctssa, has really no ally in the family, and is remarkable 

 for its crest-like casque, hardly to be distinguished from the maxilla, and is moreover peculiar 

 for the lateral grooves running its entire length. It is a Celebes form, and probably is the 

 sole survivor of a subgroup of this family. Lophoceros, the next genus, contains but two 

 species, allied closely to the members of the succeeding one, but differs in having the low casque 

 extended to a point at its anterior end, returning to the culmen by an acute angle. The last 

 genus into which I have divided the family is Tockus, containing twelve species. Some of these 



