PISCES. 329 



(3. TRYGON.) Tail slender; armed with a sharp serrated spine, but 

 without fins : head enveloped in the pectorals, which meet at an 

 obtuse angle : teeth slender, set in a quincuncial order. 



( MYLIOBJTIS.) Tail long, and extremely slender ; armed with one or more 

 serrated spines, and also furnished, near its base, with a small dorsal : 

 head projecting from between the pectorals, which last are much broader 

 transversely than in the preceding sub-genera : jaws with broad flat teeth 

 forming a pavement. 



(4. CEPHALOPTERA.) Tail long, and extremely slender ; armed with 

 a spine, and also furnished at its base with a small dorsal : head 

 truncated in front, placed between two horn-like prolongations 

 of the pectorals, which are broad as in the last sub-genus : teeth 

 small, and very slender, finely denticulated. 



ORDER IX. CYCLOSTOMI. 



Branchiae purse-shaped, fixed, opening outwards by 

 several apertures : jaws represented by an immove- 

 able cartilaginous ring, formed by the union of the 

 palatine and mandibular bones: no pectorals or 

 ventrals : body elongated : the skeleton very imper- 

 fectly developed. 



77. PETROMYZON. Seven branchial openings on 

 each side : maxillary ring armed with strong teeth ; inside 

 of the mouth furnished with tooth-like tubercles: lip cir- 

 cular: tongue with two longitudinal rows of small teeth. 



78. AMMOCGETES. Branchial openings seven in 

 number : lip semicircular, and covering only the upper 

 part of the mouth : no teeth ; but the opening of the 

 mouth furnished with a row of small branched cirri. 



79. MYXINE. Branchial openings two in number, 

 placed beneath : maxillary ring entirely membranaceous, 

 with a single tooth above : tongue with strong teeth ar- 

 ranged in two longitudinal rows on each side: mouth 

 circular, surrounded by eight barbules; a. spiracle above, 

 communicating with the interior. 



