. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. CYCLOSTOMES. 223 peculiar structures known as conodonts were regarded as myx- inoid teeth, but later these have been supposed to be annelid jaws. Traquair has recently described, under the name Pal<zo- spondyhcs gunni, a fossil from the Devonian of Scotland, which may prove to be a palseozoic marsipobranch, or possibly the-, larva of some higher form. SUB-CLASS I. PETROMYZONTES (HYPEROARTIA). Marsipobranchs with well-developed dorsal fins ; hypophysial duct closed, its external opening on the top of the head; seven branch
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. CYCLOSTOMES. 223 peculiar structures known as conodonts were regarded as myx- inoid teeth, but later these have been supposed to be annelid jaws. Traquair has recently described, under the name Pal<zo- spondyhcs gunni, a fossil from the Devonian of Scotland, which may prove to be a palseozoic marsipobranch, or possibly the-, larva of some higher form. SUB-CLASS I. PETROMYZONTES (HYPEROARTIA). Marsipobranchs with well-developed dorsal fins ; hypophysial duct closed, its external opening on the top of the head; seven branchial openings on either side; branchial basket well devel- oped ; pharyngeal region divided by a longitudinal partition into a dorsal food tube and a ventral respiratory duct from which the gill slits arise; a slightly developed spiral valve in the intestine. The lamprey eels live both in salt and in fresh water, some of the marine species ascending rivers in the spring to lay their. Fig. 228. See lamprey, Petromyzon marinus, after Goode. eggs. When ovipositing they attach themselves to stones, or take up smaller pebbles with their suckers to make their nests,, a fact which is reflected in the generic names Petromyzon and' Lampetra. The lampreys feed upon the mucus and blood which, they rasp from fishes to which they attach themselves. The lampreys are included in a single family, Petromyzonid^, and are grouped in several genera. Petromyzon, second dorsal joined to caudal, supraoral tooth with 2-3 cusps. P. marinus (sea lamprey), Europe and North America — Atlantic. Lampetra, smaller species (brook lampreys), with broad supraoral tooth with median cusp small or lacking. L. planeri, Europe. Scarcely different is L. ivilderi from New York. Other genera are Mordacia and Geotrio- from the southern Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations
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