Now, although much dispute prevails concerning the division of Fishes which should be associated with the Lampreys, yet it appears to me that no others but the narrow-mouthed Fistularidæ and Pipe-fishes can follow, since they resemble them not only in their cartilaginous bones, but in the structure also of their branchiæ. They will thus truly occupy the place of the second family. Whether the narrow-mouthed Globe-fishes are likewise to be united with them or to be set up as a third family, may seem to be matter of doubt. I adopt the first course, and arrange at present the wide-mouthed or Frog-fishes and Shads in the third family.
Fam. 1. Infusorial Fishes, Lampreys.
Body vermiform, naked, and slimy, without membral fins. Ex. Branchiostoma or Amphioxys, Myxine, Petromyzon.
In these Fishes the mouth is quite in front and round, being without maxillæ and adapted for the purposes of suction; only one nostril, but mostly several branchial foramina, which lead to cysts provided with reticular branchiæ, but without opercula.
The Branchiostomata are the smallest Fishes, not much above 1" in length, almost devoid of head, yet with traces of eyes and a nostril. The Myxinæ crawl even into the rectum of other Fishes, and live therein like Entozoa. The river or lesser Lampreys stick in the mud; the Lampreys cling fast by suction to stones, and do not draw the water in through the mouth, but through the branchial foramina themselves, like the lower animals.
Fam. 2. Polypary Fishes, Narrow-mouthed.
Body cartilaginous, mouth having maxillæ, but unusually narrow, only one branchial foramen with immoveable operculum—Fistularidæ, Pipe-fishes and Globe-fishes.
In this family we still meet with species entirely naked, but covered also with plates, scutes, nails, and spines. The corymbiform or tufted branchiæ of the Syngnathi or the Lophobranchii still remind us strongly of the cystiform reticular branchiæ of the first family.
Fam. 3. Acalephoid Fishes, Wide-mouthed.
Body naked or covered with plates; mouth in front and mostly unusually wide.