Fig. 317.—Mouth of Mordacia mordax, closed and opened.
A Lamprey (M. mordax) from the coasts of Chile and Tasmania. This fish seems to be provided sometimes with a gular sac, like the following.[47]
Fig. 318.—Mordacia mordax.
Geotria.—Dorsal fins two, the posterior separate from the caudal. Maxillary lamina with four sharp flat lobes; a pair of long pointed lingual teeth.
Two species, one from Chile and one from South Australia. They grow to a length of two feet, and in some specimens the skin of the throat is much expanded, forming a large pouch. Its physiological function is not known. The cavity is in the subcutaneous cellular tissue, and does not communicate with the buccal or branchial cavities. Probably it is developed with age, and absent in young individuals. In all the localities in which these Extra-european Lampreys are found, Ammocoetes forms occur, so that there is little doubt that they undergo a similar metamorphosis as P. branchialis.
Second Family—myxinidæ.
Body eel-shaped, naked. The single nasal aperture is above the mouth, quite at the extremity of the head, which is provided with four pairs of barbels. Mouth without lips. Nasal duct without cartilaginous rings, penetrating the palate. One median tooth on the palate, and two comb-like series of teeth on the tongue (see Fig. [101]). Branchial apertures at a great distance from the head; the inner branchial ducts lead into the œsophagus. A series of mucous sacs along each side of the abdomen. Intestine without spiral valve. Eggs large, with a horny case provided with threads for adhesion.
