Heterotis.—Cleft of the mouth rather small, with the jaws subequal; barbels none. A single series of small teeth in the jaws; pterygoids and hyoid with a patch of small conical teeth; none on the vomer or palatines.
This fish (H. niloticus), which is not uncommon in the Upper Nile and the West African rivers, exhibits several anatomical peculiarities. The fourth branchial arch supports a spiral accessory organ, the function of which is still unexplained. The air-bladder is cellular, and the stomach consists of a membranous and a muscular portion.
Twenty-Second Family—Clupeidæ.
Body covered with scales; head naked; barbels none. Abdomen frequently compressed into a serrated edge. Margin of the upper jaw formed by the intermaxillaries mesially, and by the maxillaries laterally; maxillaries composed of at least three movable pieces. Opercular apparatus complete. Adipose fin none. Dorsal not elongate; anal sometimes very long. Stomach with a blind sac; pyloric appendages numerous. Gill-apparatus much developed, the gill-openings being generally very wide. Pseudobranchiæ generally present. Air-bladder more or less simple.
The family of “Herrings” is probably unsurpassed by any other in the number of individuals, although others comprise a much greater variety of species. The Herrings are principally coast-fishes, or, at least, do not go far from the shore; none belong to the deep-sea fauna; scarcely any have pelagic habits, but many enter or live in fresh waters communicating with the sea. They are spread over all the temperate and tropical zones. Fossil remains of Herrings are numerous, but the pertinence of some of the genera to this family is open to serious doubts, as the remains are too fragmentary to allow of determining whether they belong to Salmonoids or Clupeoids. Therefore, Agassiz comprised both families in one—Halecidæ. Many of the remains belong to recent genera, which are readily recognised, as Clupea, Engraulis and Chanos, principally from the schists of Glaris and Licata, from Monte Bolca and the Lebanon. Others, like Thrissopater, from the Gault at Folkestone, Leptosomus, Opisthopteryx, Spaniodon, from the chalk and tertiary formations, can be readily associated with recent genera. But the majority do not show an apparent affinity to the present fauna. Thus, Halec from the chalk of Bohemia, Platinx and Coelogaster from Monte Bolca, Rhinellus from Monte Bolca and Mount Lebanon, Scombroclupea, with finlets behind the anal, from the Lebanon and Comen, and Crossognathus from tertiary Swiss formations, allied to Megalops, Spathodactylus from the same locality, and Chirocentrites from Mount Lebanon, etc. Finally, a genus recently discovered in tertiary formations of Northern Italy, Hemitrichas, has been classed with the Clupeoids, from which, however, it differs by having two short dorsal fins, so that it must be considered, without doubt, to be the representative of a distinct family.
Engraulis (including Cetengraulis).—Scales large or of moderate size. Snout more or less conical, projecting beyond the lower jaw. Teeth small or rudimentary. Intermaxillaries very small, hidden; maxillary long, attached to the cheek by a scarcely distensible membrane. Anal fin of moderate or great length. Branchiostegals short, from nine to fourteen in number.
Not less than forty-three different species of “Anchovies” are known from temperate and tropical seas. They exhibit marked differences in the length of their maxillary bone, which sometimes does not reach the gill-opening, whilst in other species it extends far beyond it; and in the number of their anal rays, which varies from 20 to 80. Some have the upper pectoral ray prolonged into a filament, thus leading towards the succeeding genus, Coilia. The majority are recognised, besides, by their peculiar structure, by a broad silvery, lateral band, similar to that observed in the Atherines. The most celebrated Anchovy is E. encrasicholus, very plentiful in the Mediterranean, but rarely wandering northwards. It is the species which, preserved in salt, is exported to all parts of the world, although similarly lucrative fisheries of Anchovies might be established in Tasmania where the same species occurs, in Chile, China, Japan, California, at Buenos Ayres, each of which countries possesses Anchovies by no means inferior to the Mediterranean species.
Coilia.—Body terminating in a long tapering tail. Scales of moderate size. Snout and jaws as in Engraulis. Anal fin exceedingly long, confluent with the caudal. The two or three upper pectoral rays are much prolonged, and their branches form four, six, or seven filaments.
Fig. 300.—Coilia clupeoides.