MAILED TUBE-MOUTHS. 423 



In the single dorsal fin the spinous portion usually exceeds the soft in extent ; the 

 anal fin having three or more spines, and its rayed portion being similar to the 

 soft dorsal. The jaws are provided with small teeth, but the palate is smooth ; 

 and the number of gills is four, In some species the teeth are lobate and the 

 intestines complicated by many foldings; these types being vegetable -feeders 

 while all the remainder are carnivorous. Among the best known representatives 

 of the typical genus Chromis is the so-called butti of the Nile (C. niloticus), which 

 is one of the largest members of the family ; while Tristram's chromid (G. tristrami) 

 here figured is from salt and other lakes in the Sahara and Ashanti. As a genus, 

 Chromis is distinguished by its lobate teeth, the presence of only three spines in 

 the anal fin, and the scaly gill-cover ; and it therefore belongs to the vegetable- 

 feeding group. Nineteen existing genera have been described; and the family 

 appears to be represented by one, or perhaps two extinct generic types from the 

 middle Eocene of Monte Bolca, in Italy. 



The Tuft-Gilled and Comb-Gilled Fishes, — Suborders 



LOPHOBRANCHII AND PlECTOGNATHI. 



The two small subordinal groups of fan -finned fishes now to be noticed 

 have been generally placed after the soft -finned fishes, but from recent 

 investigations into their anatomy it appears more probable that they are highly 

 specialised types related to the spiny-finned group. 



The Mailed Tube-Mouths,— Family Solenostomatid^e, 



A few small fishes from the Indian Ocean constituting the genus Solenostoma 

 are the sole representatives of the first family of the suborder Lophobranchii ; the 

 distinctive features of that subordinal group being as follows. The body is 

 invested in a segmented bony dermal skeleton, and the bones of the gill-cover are 

 reduced to a single plate. The gill-openings are small, and the gills themselves 

 consist of small, rounded tufts springing from the gill -arches; while the 

 muscular system is characterised by its very slight development. The simple air- 

 bladder, when present, resembles that of the spiny-finned group in being unpro- 

 vided with a duct communicating with the pharynx ; and the prolonged muzzle 

 terminates in a small toothless mouth, in which the bones are arranged as in the 

 group last named. In the family under consideration the gill-openings are wide ; 

 the rays of the first of the two dorsal fins are not articulated ; and the whole of the 

 other fins are well developed. The mailed tube-mouths take their title from the great 

 elongation of the tube-like muzzle ; the compressed body having a very short tail, 

 and, like the head, being covered with a thin skin, beneath which are the large 

 bony plates, marked with a radiate pattern. The soft dorsal and anal fins arise 

 from boss-like elevations of the hinder part of the body ; the pelvic fins, which are 

 placed close together in the same vertical line as the tall first dorsal, and have seven 

 rays, are separate from one another in the males, but in the opposite sex have their 

 inner edges joined to the skin of the chest so as to form a pouch for the reception 

 of the eggs. The air-bladder is wanting. A female of the blue-finned species (S. 



