58 BOARD OF AGRICULTURE. 



on the dorsal aspect of the head ; the scapular arch complete ; naso- 

 pectoral car tillages present ; no eye-lid, or only an aduate upper 

 one. 



Order Holocephali ; Bona. 

 There are but one or two genera of fishes belonging to this order. 

 The Chimcera, or sea monster of the high northern seas, is embraced 

 by it. None of them, to our knowledge, have been found on the 

 coast of Maine. They have but one branchial, or gill aperture on 

 each side of the head, as in the perfected or true fishes. 



The next step in the descending series brings us to the 

 Sub-class Dermopteri ; Owen. 



This is the lowest and most simply constituted of all the classes 

 of the fishes. The body is very much elongated and worm-like, 

 either sub-cylindrical or compressed. The endo-skeleton is very 

 rudimentary and cartilaginous, and in one of the orders, (Pha- 

 ryngobranchii,) there is no distinct head. The pectoral and ven- 

 tral fiTis are both absent. The skin is entirely naked and mucous, 

 and the fins are only folds of the skins. There is no pancreas and 

 no air bladder. The olfactory organ and nostril are single. 



There are three orders to this class, viz : 



Order IIyperoarth ; (Bona.) Midler. 

 The body of the members of this order is invariably greatly 

 elongated, and sub-cylindrical or anguiliforni. The head is dis- 

 tinct. The "myelon," or medulla spinalis, is described by Owen 

 as being flattened or depressed, "of opaline sub-transparency, 

 ductile and elastic." The hulbus arteriosus is absent, but there 

 are two opposite valves at the organ of the branchiae vessel, as in 

 the Teleostei. The branchiae are purse shaped and without opcr- 

 cula. There are seven in number on each side. Each receives the 

 streams of water for the correction of the blood, through short 

 tubes, entering from a medium canal, which is below and distinct 

 from the oesophagus and which terminates behind in a closed wall, 

 and according to Professor Owen, communicates with the fauces 

 anteriorly "by an opening guarded by a double membranous 

 valve." This order includes the well known "Lampcr Eel," and 

 is equivalent to the Marsipobranchii, (purse gills,) of other 

 authors. 



