326 



Div. 1. "^^ERTEBRATE ANIMALS.— PISCES. 



Class 4. 



Order YII.— LOPHOBRA>'CniI. 



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

 bladder without air duct. 



Family.— Bippocampidcz. i:«ample.— Sea-horse. Family.— SyngnatUda:. £ii;ampfe.— Pipe-fish. 



Oedeb 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.- 



. . „ , fLepidosteus. 

 ■SaUmandroideu Example.— J „ , . 



liolypterus. 



Pycnodontidco. 

 Lepidoidei. 



Pycnodus. 

 Dapedius. 



Family. — Slurionidm. 

 Acanthodei. 

 DipteridcB. 

 Cephalaspidco. 



Example. — Sturgeon. 



Acanthodes, 



Dipterus. 



Ccphalaspio. 



Ohdee IX.— PllOTOPTEUI. 



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, 



[,Vi?.— This curious animal, for the reception of which this order lias 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 thoir margins; a single external gill aperture ; no 

 &wini bladder ; intestine with spiral valve. 



Family.— Chimxeroidci. £xaOT;)I<;.— Chimeera. Family.— EdapJiodontidce .Earan!;;?^.— Edaphodon. 



Ordeb. XI.— PLAGIOSTOMI. 



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

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

 spirttl valve. 



Family. 

 ITybodontidoe. 

 Cestraeioniidce. 

 Kotodanida:. 

 SpiitacidcB. 

 ScyUiidcB. 

 Nictitantes. 

 Lamnidce. 

 Alopeeiido}. 

 Scymniida;. 



Example. 

 Iljbodus. 

 Cestracion. 

 Gray-shark. 

 Piked Dog-fish. 

 Spotted Dog-fish. 

 Tope. 

 Porbeagle. 

 Fox-shark. 

 Greenland-shark. 



Family. 



Squatina:. 



Zyyccnidce, 



Prislldas. 



lildnobaiidcc, 



7'orpedinidce. 



liaiidce. 



TrygonidcB. 



Myliobatida;. 



Ccphahptcridce. 



Example. 

 ilunk-fish. 

 Ilaiumei'head-shark, 

 Saw-fish. 

 Rhinobates. 

 Electi'ic-ray. 

 Ray, or Skate. 

 Sting-ray, or Fireflaire. 

 E;ig!e.ray. 

 Cephaloptera. 



The additional information recently gained respecting the curious little Ampldoxus or Lancelet (p. 331), has left 

 no doubt as to its claim to he regarded as a fish ; but its peculiarities of organization arc 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, wo find numerous bulb-like enlargements scattered over the system of blood- 

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

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

 through thugill-chambcrs 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 poro." This arrangement closely corresponds to that 

 which exists in the Ascidian Mollusks. The alimentary canal is lined with cilia; 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 

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

 from some of the Batrachian Rciitiles. 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 uo fossil traces of their existence. 



