The remarkable little Fish, Phractolaemus ansorgii, discovered by Dr. W. J. Ansorge in the Niger Delta in 1900, and which has since also been found in the Congo, stands quite apart among the Malacopterygians, its nearest allies being apparently the Osteoglossidae. The body is elongate and subcylindrical, covered with large striated scales; the head is small, the skull strongly ossified, covered with thin skin; the mouth small, proboscidiform, capable of being thrust forwards, when at rest folded over and received into a depression on the upper surface of the head; the narial orifice is single, and preceded by a barbel; the gill-openings are narrow, restricted to the sides. The ventral fins are inserted far back, the dorsal and anal are short. The air-bladder is very large, and the intestine extremely long and much convoluted. Vertebrae 26 + 8.
Fam. 14. Saurodontidae.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly united to the former; these bones, as well as the mandible, with teeth implanted in deep sockets; palate toothless. Supraoccipital separating the small parietals; opercular bones well developed; symplectic present, exposed. Basis cranii double. Ribs sessile, very low down on the centra; no parapophyses; neural arches not fused with the centra. Pectorals inserted very low down; postclavicle apparently absent. Caudal fin deeply forked, without fused hypurals.
This family, comprising several Cretaceous genera, may be regarded as ancestral to the Chirocentridae, with or near which it has been placed by Cope and various later authors. The normal position of the symplectic, however, entitles its members to rank as a separate family, and the autogenous neural arch, as well as the distinctness of the bones supporting the caudal fin, are also indicative of a greater generalisation. The restoration of Ichthyodectes as given by Loomis, shows a general form similar to an ordinary Herring, but it does not appear to be reliable.
The members of the Saurodontidae have been referred to two groups: (a) with praedentary (praesymphysial) bone, Saurocephalus, Saurodon; (b) without praedentary, Chirocentrites, Portheus, Ichthyodectes, Spathodactylus, Cladocyclus. These Fishes are from the Chalk of Europe and North America, and some among them attain a very large size, perhaps not less than two metres in length.
Fam. 15. Chirocentridae.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries, the latter the more developed and firmly united to the former; these bones, as well as the mandible, with large teeth not implanted in true sockets; minute teeth on the palatines, pterygoids, and hyoid bones, Supraoccipital in contact with the frontals, separating the small parietals; opercular bones well developed; symplectic hidden between the inner surface of the quadrate and a descending process of the hyomandibular. Basis cranii double. Ribs very slender, sessile, very low down on the centra; no parapophyses; epipleurals and epineurals. Pectorals inserted very low down. Post-temporal forked; postclavicle absent; a thin bony lamina, similar to the postclavicle, above the pectoral fin, attached to the scapula; scapular foramen in scapula; coracoids in contact with each other, forming a keel. Ventrals very small, with 7 rays. Brachiostegal rays 8. Air-bladder large, not communicating with the ear, incompletely divided into cells. Mucous membrane of the intestine forming a spiral fold.
The body is very elongate and strongly compressed, covered with thin, deciduous scales; the vertebrae number 75. The dorsal fin is short and opposite to the anal, which is long.
Fig. 340.—Side view of skull and pectoral arch of Chirocentrus dorab.
Chirocentrus dorab, the only representative of this family, inhabits the Indian Ocean and the seas of China and Japan.
Fam. 16. Clupeidae.—Margin of the upper jaw formed by the praemaxillaries and the maxillaries. Supraoccipital separating the small parietals; opercular bones well developed. Basis cranii double. Ribs mostly sessile, inserted behind parapophyses; intermuscular bones (epineurals, epipleurals, adpleurals) usually numerous. Post-temporal forked, the upper branch attached to the epiotic, the lower to the opisthotic; post-clavicle applied to outer side of clavicle. Ventrals with 6 to 11 rays. Air-bladder large, communicating with the ear.