SCYLLIUM. FISHES. 383 



maxillary ring. 2 or 3 feet long. Inhabits European Seas. B. 

 Shaw, v. pi. 133. 



This species ascends in spring into the mouths of rivers. 



P. Jluvialilis, Lin. The Lesser Lamprey. Silver- coloured, black- 

 ish,, or olive- coloured on the back; the first dorsal fin distinct 

 from the second ; two large teeth at the top of the maxillary ring. 

 12 to 18 inches long. Rivers. B Pen. Brit. Zool. iii. pi. 10. 



P. Planeri, Bloch. Body olive-coloured above, paler below ; two 

 large teeth in the upper part of the maxillary ring ; dorsal fins 

 contiguous or united. Inhabits fresh waters in Germany. Cuv. 

 Reg. An. ii. 119. 



Gen. 2. AMMOCOSTES, Dum. Petromyxon, Lin. 

 Body soft and membranous; branchial openings nearly the same 

 as in the lampreys ; lip semicircular, and covering only the 

 upper part of the mouth ; no teeth ; dorsal fins united to the 

 caudal one, forming a low and sinuous ridge. 



A. branchialis, Cuv. The Common Pride. Body marked with 

 transverse lines ; tail lanceolate. 6 to 8 inches long. Inhabits 

 Rivers. B. Pen. Brit. ZooL iii. pi. 10. 



Gen. 3. GASTROBRANCHUS, Bloch. Myxine, Lin. 

 Maxillary ring membranous, with only one tooth above ; late- 

 ral dentations of the tongue strong, and in two rows on each 

 side ; two spiracles under the abdomen. 



Linnaeus placed the animal which forms the type of this genus in his class Vermes, 

 though its organization is analogous to that of the lamprey, except in regard to the 

 branchial openings, which in this genus, in place of an outward aperture, open into 

 a common canal on each side, and these two canals terminate in two apertures situ- 

 ate under the belly. The mouth is circular, surrounded with eight cirri, and at its 

 superior margin is an opening which leads into the interior. The body is cylindri- 

 cal, and furnished with a fin on the hinder part, which surrounds the tail. It has 

 no eyes. Through the lateral pores of this singular animal a mucous fluid exudes 

 in great abundance. 



G. coccus, Bloch. (M . glutinosa, Lin.) Glutinous Hag. Body whit- 

 ish, reddish towards the head and tail; a double row of lateral 

 pores. 4 to 6 inches long. European seas. B Shaw, v. pi. 134. 



G. Dombeyi, Lacep. Head rounded, broader than the body. In- 

 habits South American Seas Shaw, v. 267- 



ORDER II. PLAGIOSTOMI, Dumeril. Selachii, Cuv. 



Branchiae pectinated, the openings numerous, without operculi 

 or membranes ; palatine and postmandibulary bones armed 

 with teeth in place of jaws. 



The ordinary bones of the jaws in this family are merely rudimentary. One 

 single bone connects these jaws to the cranium, and supplies the place of the tympa- 



