664 



PISCES. 



Okder VII.— lofhobranciiii. 



Internal skeleton partially ossified; external skeleton ganoid; gills tufted ; opercular aperture small ; swim- 

 bladder without air duct. 



Family.— Eippocampidai. iTxample.— Sea-horse. Family.— Syngiuxthidce. £xamj>f«.— Pipe-fish. 



Okder VIII.— GANOIDEI. 



Internal skeleton in some osseous, in some cartilaginous, in some partly osseous partly cartilaginous; external 

 skeleton ganoid ; fins usually with the first ray a strong spine ; a swim-bladder and air duct. 



Family. — Salamandroidei. Example.- 



Pycnodontidcc. 

 Lepidoidei. 



( Lepidosteus. 

 ' Polypterus. 



Pycnodus. 



Dapedius. 



Family. — Shirionidce. Example. — Sturgeon. 



Acantliodei. Acanthodes. 



DipteridoB. Dipterus. 



Cephalaspidce. Cephalaspis. 



Order IS.— PROTOPTERI. 



Internal skeleton partly osseous, partly cartilaginous; external skeleton as cycloid scales; pectorals and 

 ventrals as flexible filaments ; gills filamentary, free ; no pancreas ; swim-bladder as a double lung, with air duct, 

 intestine with a spiral valve. 



Family. — Sirenoidei. Example. — Lepidosiren, 



[NB. — This curious animal, for the reception of which this order has been constituted, combines in a very 

 remarkable degree the characters of the Fish and of the Reptile, and has been placed by many naturalists in the 

 latter class.] 



Order X.-nOLOCEPHALI. 



Internal skeleton cartilaginous ; external skeleton as placoid granules ; most of the fins with a strong spine for 

 the first ray ; ventrals abdominal ; gills laminated, attached by their margins ; a single external gill aperture ; no 

 swim bladder ; intestine with spiral valve. 



Family. — Chinccroidei. Example. — Chimsera. Family. — Edaphodontidce Example. — Edaphodon. 



Obdeb. XI.— PLAGIOSTOMI. 



Internal skeleton cartilaginous, or partially ossified ; external skeleton placoid ; gills fixed with five or more 

 gill apertures ; no swim bladder ; scapular arch detached from the head ; ventrals abdominal ; intestine with 

 spiral valve. 



Family. 

 Hybodontidoc. 

 CestraciontidcB, 

 NotodanidcE. 

 Spinaddcs. 

 ScyUiidcB. 

 NictitanUs. 

 Lamnidw. 

 Alopeciida;. 

 Scymniida:. 



Example. 

 Iljbodus. 

 Cestracion. 

 Gray-shark. 

 Piked Dog-fish. 

 Spotted Dog-fish. 

 Tope. 

 Porbeagle. 

 Fox-shark. 

 Greenland-shark. 



Family. 

 Sqiuitince. 

 Zygoenidoe. 

 Pristidce. 

 Bhindbatidce. 

 Torpedinidce. 

 RaiidcB. 

 Trygonidce. 

 Myliobatidce. 

 Cephalopteridce. 



Example. 

 Monk-fish. 

 Ilammerhead-shark. 

 Saw-fish. 

 Rhlnobates. 

 Electric-ray. 

 Ray, or Skate. 

 Sting-ray, or Fireflaire. 

 Eagle-ray. 

 Cephaloptera. 



The additional information recently gained respecting the curious little Amphioxus or Lancelet (p. 334), has left 

 no doubt as to its claim to be regarded as a fish ; but its peculiarities of organization are such as to separate it 

 completely from all other members of the class. The nervous system consists almost solely of a spinal cord, with 

 scarcely any traces of a brain or of organs of sense ; and this is enclosed in a fibrous sheath, the only represen- 

 tative of the vertebral column. This sheath, with a series of fine transparent threads of cartilage on either side, 

 representing the ribs, and with a framework around the pharynx, constitutes the entire skeleton; of a proper 

 cranium there is not the slightest vestige. The blood is colourless, like that of Invertebrata ; and instead of 

 a single heart for its propulsion, we find numerous bulb-like enlargements scattered over the system of blood- 

 vessels, reminding us of the circulating apparatus amongst the inferior Worms. The water which is taken in for 

 respiration, and which passes through the slits iu the dilated pharynx, is not thence transmitted directly outwards 

 through the gill-chambers by orifices in the neck ; but is sent into the general cavity of the abdomen, from which 

 it finds its way out by a single aperture, the "abdominal pore." This arrangement closely corresponds to that 

 which exists in the Ascidian MoUusks. The alimentary canal is lined with ciha; there is no distinct trace of a 

 liver. Thus the Lancelet is quite isolated from all other existing fishes ; being removed even from the group of 

 Cyclostomi to which it is most nearly allied, by differences which are greater than those which separate fishes 

 from some of the Batrachian Reptiles. Perhaps we are to regard it as a relic of some order of fishes now all but 

 extinct, which, in consequence of the softness of their skeletons, have left no fossil traces of their existence. 



