ORDER X. 



DERMOPTERI. 



The body is vermiform or worm-like to such a striking extent that Linnaeus himself got de- 

 ceived, placing one of the species in the class of worms. This external resemblance to worms 

 is rendered the more deceiving as the lateral fins (pectorals and ventrals) are altogether wanting, 

 the skin naked or scaleless, either verticillated or annulated. Tlie vertical fins themselves are 

 reduced to a mucous fold of the derm or skin, which is moreover mucous throughout. The 

 internal skeleton being unossified, without distinct vertebrse, instead of which a central carti- 

 laginous cord, and the head so much blended with the body that in various cases it is not easily 

 distinguishable. The pancreas and air bladder, both, are absent. The intestine is straight, 

 witliout either fold or appendages. 



Stn. — Dermopteri, Owew, Lect. Corap. Anat. Vertebr. anim. 184G, 47. — Bd. Iconogr. Encycl. II, 1850, 203. 

 ChondrlclUhes Irematopnes, Ddm. Ichthyol. aiialyt. 1856, 104. 



The Dermopterians subdivide into two sub-orders ; the Pliaryngdbranchii seu Cirrhostomi 

 and the Marsipohranchii seu Gyclostomi. 



The Cirrhostomians constitute but one family, that of Amphioxidae (Lancelet), which has 

 no representatives in North America. 



SUB-ORDER. 



MARSIPOBRANCHII s. GYCLOSTOMI. 



The heart is extant, but the accessory arterial heart, known as the hulbus arteriosus, is wanting. 

 The Iruncus arteriosus consists merely of the ordinary membranes which enter into the structure 

 of the arteries. The gills are fixed, inclosed within cavities either simple or multipartite, 

 receiving the respiratory streams through apertures usually numerous and lateral. 



SvN. — Marsipohranchii, Bonap. Syn. Vert. Sysl. 1837, 43. 



J\Iarsipobranchii s. Cyclostomi, Mull, in IVcigm. Archiv fiir Naturg. 1845, I, 137. — Owen, Loct. Comp. Anat. 



Vertebr. anim. 1846, 48. 

 Exolremes. — Don. Ichthyol. analyt. 1856, 110. 



The Cyclostomians constitute two families; that of Myxinidae (Myxine, Hag, or Borer), 

 which is not represented in the ichthyic fauna of North America, and that of the Lampreys, 

 which follows. 



Family PETROMYZONTIDAE, Owen. 



The general form of the body is elongated, cylindrical, or sub-cylindrical, eel-shaped. The 

 dorsal, caudal, and anal fins are continuous ; the gills fixed or immovable, and situated in a 

 sort of chest. There are seven lateral branchial openings on either side, admitting the water 

 to bathe the gills. A single spiracle situated on the upper surface of the head. 



