THE SURGEONS 2731 



Two extinct genera, namely, Paltzorhynchus from the Eocene of 

 ' Switzerland and Hemirhynchus from the Oligocene of France, repre- 

 sent a separate family (PalcEorhynchidce} , distinguished from the last 

 by the production of the muzzle into a long beak, which may be either provided 

 with small teeth or toothless. The dorsal fin occupies nearly the whole length of 

 the compressed body, and the anal fin is also elongated, and extends nearly to the 

 forked caudal. 



THE SURGEONS Family ACRONURID^ 



With this family we come to a group of spiny-finned fishes, including some 

 thirteen others, which present the following characteristics in common: The dorsal 

 fins are either placed together or continuous, the spinous portion being, when fully 

 developed, shorter than the soft part, while it may be modified into tentacles, 

 detached -spines, or an adhesive disc; and the anal is similar in characteristics 

 to the soft dorsal, and in some instances both these fins are modified posteriorly 

 into finlets. The pelvic fins, if developed, are always thoracic or jugular in 

 position, and are never modified into a sucker; and there are no papillae in the 

 neighborhood of the vent. Nearly the whole of the members of the group are 

 marine. 



The first family is typified by a genus (Acronurus*) the representatives of which 

 are popularly known by the name of ' ' surgeons, ' ' owing to the presence of a sharp 

 lancet-like spine on each side of the tail in the adult. In addition to the presence 

 of one or more such spines or bony plates, the family is further characterized by a 

 single dorsal fin, with a very small number of spines. The body is compressed and 

 oblong or deep in form, with a covering of minute scales; the moderate-sized eyes 

 are lateral in position; the small mouth is furnished in front with a single series of 

 more or less compressed upper and lower incisors, which may be either pointed or 

 serrated; but the palate is toothless. The pelvic fins are thoracic in position, and 

 the hinder extremity of the air bladder is forked. These fishes are inhabitants of 

 all the tropical seas, and are most common in the neighborhood of coral reefs and 

 islands, where some feed on the soft polyps of the coral, but others on various 

 vegetable substances. In the true surgeons (Acronurus') there is an erectile spine 

 situated in a groove on each side of the tail, and the pelvic fins are generally 

 furnished with a single spine and five rays. In the young the body is scaleless, 

 and the tail spines either very small or wanting. These fishes are represented by a 

 large number of species, the largest of which does not exceed eighteen inches in 

 length, and they are distributed over all tropical seas with the exception of the 

 Eastern Pacific. In a fossil state the genus, like the next, occurs in the middle 

 Eocene beds of Monte Bolca, in Italy. From the true surgeons the members of the 

 genus Naseus, which range over the tropical Pacific and the Indian Ocean, are 

 distinguished by having from one to three nonerectile spines on each side of the 

 tail, and the presence of only three rays in the ventral fins; while in some forms 

 the head is armed with a forwardly-directed bony horn or crest-like prominence. 



