One living genus only is known, which was preceded in the tertiary epoch by Solenorhynchus (Monte Postale).
Solenostoma.—Snout produced into a long tube. Body compressed, with very short tail. All parts covered with thin skin, below which there is a dermal skeleton formed by large star-like ossifications. The soft dorsal and anal fins on elevated bases; caudal fin long. Ventral fins inserted opposite to the anterior dorsal, close together, seven-rayed; they are free in the male, but in the female their inner side coalesces with the integuments of the body, a large pouch for the reception of the eggs being formed thereby. Air-bladder and pseudobranchiæ absent. Branchiostegals four, very thin. Intestinal tract very simple, with a stomachic dilatation, without pyloric appendages. Ova very small.
The dermal skeleton of this singular type is formed by star-like ossifications, four in each horizontal and vertical series on the side of the fore part of the trunk; each consists of four or three radiating branches by which it joins the neighbouring bones; on the hind part of the trunk and tail the series are diminished to two. The dorsal and abdominal profiles in front of the fins are protected by similar bones. The vertebral column is composed of eighteen abdominal and fifteen caudal vertebræ, the vertebræ gradually decreasing in length backwards, so that the shortness of the tail is caused not only by the smaller number of vertebræ, but also by their much lesser length. Neural and hæmal spines are developed. The pelvis consists of two pairs of cartilaginous laminæ, the convex margin of the anterior fitting into an angle of a dermal bone which separates the pelvis from the well-ossified humeral arch.
The singular provision for the retention and protection of the eggs has been described above (p. 162, figs. 73 and 74), and we have only to repeat here that it is the female which takes care of the progeny, and not the male as in the following family. Two or three small species are known from the Indian Ocean; they are beautifully marked, especially the male, which also appears to be of smaller size in this genus than the female.
Second Family—Syngnathidæ.
Gill-openings reduced to a very small opening near the upper posterior angle of the gill-cover. One soft dorsal fin; no ventrals, and, sometimes, one or more of the other fins are also absent.
Small marine fishes, which are abundant on such parts of the coasts of the tropical and temperate zones as offer by their vegetation shelter to these defenceless creatures. They are bad swimmers (the dorsal fin being the principal organ of locomotion), and frequently and resistlessly carried by currents into the open ocean or to distant coasts. All enter brackish water, some fresh water. The strata of Monte Bolca and Licata (Sicily) have, yielded evidence of their existence in the tertiary epochs; beside species of Siphonostoma and Syngnathus (Pseudosyngnathus), remains of an extinct genus, Calamostoma, allied to Hippocampus, but with a distinct caudal fin, have been found. On their propagation see p. 163, Fig. [76].
A. Syngnathina.—The tail is not prehensile, and generally provided with a caudal fin.—Pipe-Fishes.
Siphonostoma.—Body with distinct ridges, the upper caudal ridge continuous with the lateral line, but not with the dorsal ridge of the trunk. Pectoral and caudal fins well developed; dorsal fin of moderate length, opposite to the vent. Humeral bones movable, not united into a “breast-ring.” Males with an egg-pouch on the tail, the eggs being covered by cutaneous folds.
Two species, of which S. typhle is common on the British, and generally distributed on the European coasts.