=The Haplomi.=—In the groups called _Iniomi_ and _Lyopomi_, the mesocoracoid arch is imperfect or wanting, a condition which in some cases may be due to the degeneration produced by deep-sea life. In the eels a similar condition obtains. In the group called _Haplomi_ (ἁπλοός, simple; ὤμος, shoulder), as in all the groups of fishes yet to be discussed, this arch is wholly wanting at all stages of development. In common with the _Isospondyli_ and with soft-rayed fishes in general the air-bladder has a persistent air-duct, all the fins are without true spines, the ventral fins are abdominal, and the scales are cycloid. The group is a transitional one, lying almost equidistant between the _Isospondyli_ and the _Acanthopterygii_. Gill unites it with the latter and Woodward with the former. We may regard it for the present as a distinct order, although no character of high importance separates it from either. Hay unites the _Haplom_i with the _Synentognathi_ to form the order of _Mesichthyes_, or transitional fishes, but the affinities of either with other groups are quite as well marked as their relation to each other. Boulenger unites the _Iniomi_ with the _Haplomi_, an arrangement which apparently has merit, for the most primitive and non-degenerate _Iniomi_, as _Aulopus_ and _Synodus_, lack both mesocoracoid and orbitosphenoid. These bones are characteristic of the _Isospondyli_, but are wanting in _Haplomi_. There is no adipose dorsal in the typical _Haplomi_, the dorsal is inserted far back, and the head is generally scaly. Most but not all of the species are of small size, living in fresh or brackish water, and they are found in almost all warm regions, though scantily represented in California, Japan, and Polynesia. The four families of typical _Haplomi_ differ considerably from one another and are easily distinguished, although obviously related. Several other families are provisionally added to this group on account of agreement in technical characters, but their actual relationships are uncertain. =The Pikes.=—The _Esocidæ_ have the body long and slender and the mouth large, its bones armed with very strong, sharp teeth of different sizes, some of them being movable. The upper jaw is not projectile, and its margin, as in the _Salmonidæ_, is formed by the maxillary. The scales are small, and the dorsal fin far back and opposite the anal, and the stomach is without pyloric cæca. There is but a single genus, _Esox_ (_Lucius_ of Rafinesque), with about five or six living species. Four of these are North American, the other one being found in Europe, Asia, and North America.