ICHTHYOLOGY. 



Classifica- 

 tion — 

 Lopho- 

 branchs. 



with the other Ganoids in the valves and mnscnlarity of the 

 arterial trunk, and in the spiral intestinal valve, Miiller in- 

 fers that it will be found also to possess a chiasma of the 

 , optic nerves (no decussation), a thymus gland, and an 

 uncleft retina. He concludes by saying that it cannot be xe- 

 i'evvQiX ittxihev io \\\G Lepidosteini or Polf/pferim^ being sepa- 

 rated from the former by the absence oi fulcra, and from 

 the latter by not possessing the dorsal polyptery; and he 

 therefore regards it as the living representative of a peculiar 

 family of Ganoids, and finds analogous genera in the fossil 

 3Iegalurus, Leptohpis^ 77inssops, and tlieir allies. All of 

 these have soft scales, an osseous vertebral column, and a 

 similarity in form of body and structure of fins. Questions 

 of such interest to ichthyologists have doubtless long ago 

 been solved by Agassiz, who has such ready access to many 

 species of Amia, but the results of his investigations have 

 not reached us. Cuvier compared the air-bladder of Amia 

 to the lung of a reptile on account of its great cellular sub- 

 division ; and in his list of affinities or analogies above 

 quoted, M. Valenciennes miglit have added the similarity 

 of the air-bladder of the Amice to those of Erythrinus, or 

 of the Siluroid Bagrus^ which have that viscus subdivided 

 by transverse septa. 



The Sturgeons are very abundant in the rivers of Si- 

 beria which flow to the southward, and no less so on 

 both sides of North America. They do not inhabit any 

 of the rivers of that country which flow into the Arctic 

 Sea, and consequently are not found to tlie N. of the 

 watersheds between the o3d and 54th parallels of lati- 

 tude, where the mean temperature of tlie year is about 

 33° of Fahrenheit's scale. They seldom enter clear cold 

 streams, but in the season ascend the muddy rivers in vast 

 numbers, so that many populous native tribes subsist wholly 

 on the Sturgeon fishery during the summer. In most loca- 

 lities two forms are readily recognised by the comparative 

 length and acuteness, and shortness and bluntness, of their 

 snouts ; but every watershed has its own species, varying 

 in the osseous shields, positions of the rostral barbels, form 

 of the tail, fins, and other characters. 



Ordek VIII.— GAXOIDEI, Mull. 



Endo-skeleton in some osseous, in some cartilaginous, in some 

 partly osseous partly cartilaginous; exo-skeleton ganoid. Fins 

 usually with the first ray a strong spine. A swim-bladder and 

 air-duct. Numerous valves in the arterial trunk. No decussation 

 of the optic nerves. Free gills and opercula, and abdominal ventral 

 fins. 



Family I — LEPIDOSTEID^. 



Lepidosteini, MiiU. Upper jaw composed of several pieces; the 

 vomer divided in two by a median cleft; the basisphenoid is con- 

 fluent with the basioccipital ; the nasal bone dentiferous; the 

 mandible composed of as many pieces as in Reptiles; the ver- 

 tebrae articulated by ball and socket; the olfactory organ, situ- 

 ated at the extremity of the greatly elongated jaw, contains the 

 ordinary nasal folds which are arranged simply; a respiratory 

 opercular gill is present as well as a pseudobrancliia, but no 

 blowing hole. The gills on the four arches have the perfect bi- 

 foliate structure, and behind the last arch and the hyoid hone there 

 exists, as usual, a fissure. Jlranchiostegals three, the membrane 

 passing from side to side like a muntle. and undivided. Anterior 

 edge of all the fins protected by two rows of spinous scales. Fin- 

 rays all articulated ; caudal fin abruptly truncate, its rays inserted 

 partly at the extremity of the vertebral column, partly beneath it. 

 Stomach not csecal ; several pancreatic c;vca; no spiral valve in 

 the intestine ; swim-bladder cellular, containing trabcculm carnecc 

 between the cell divisions, and opening by a long slit into the up- 

 per wall of the throat. 



Genus I. Lepidosteus, Lacep. An elongated snout varying 

 in breadth in different species, formed of the premaxillaries, niax- 

 illaries, palatines, nasal, and vomer ; mandible equal to it in length ; 

 both covered on their surfaces with raduliform teeth and bordered 

 by a row of long pointed ones. Ten species, American, 



Family II.— POLYPTEKIDiE. 



PolypUrini, MiiU. The upper jaw is not divided into pieces, the 



vomer is single, and the mandible and skull generally are constructed Classifioa- 

 as in other osseous fishes. A labial cartila<fe exists at the corner tion — 

 of the mouth, supporting the upper and under lips. The fourth gill Sirenoids. 

 is only unifoliate, and there is no slit behind it. ; the opercular gill \. ^ -^ ^ 

 is wanting, and no pseudobrancliia ever occurs ; but there is a 

 blowing hole on each side, covered bv an osseous valve. The in- 

 ferior pharyngeal bones are wanting. A series of separate fins 

 extends along the back, each consisting of a spine and a plume of 

 articulated rays behind it. The rounded caudal and the anal are 

 composed of jointed rays, which in the former are inserted above 

 as well as below the spines ; the pectoral has a somewhat elon- 

 gated scaly Jirab. The nostrils are more complicated than in any 

 other fish. In a large cavity there is a labyrinth of five nasal 

 passages, each with a gill-like arrangement of folds ; anterior nos- 

 tril prolonged into a membranous pipe; the posterior one a small 

 cleft anterior to the eye. The stomach is csecal, and there is a 

 pancreatic caecum. The intestine contains a spiral valve; swim- 

 bladder double, consisting of two sacs difl^ering in length, and 

 opening into a short common cavity that communicates with the \ 

 ventral floor of the throat by a long fissure. ' 



Genus 1. Polypterus, Geoff. Three species, Nile, Senegal, 

 Tchadda. 



Family III.— AMIID^. 



Genus I. Amia, Linn. Excepting in the absence of lingual 

 teeth, the mouth of an Amia is that of a Trout. Head covered with 

 a very thin mucous skin, easily removed, and then the naked cra- 

 nium, supratemporals, suborbitar scale bones, and operculum ap- 

 pear as sculptured bony plates. The sublingual bone is naked and 

 furrowed. Upper part of the snout smooth and fleshy ; inferior 

 lip large and thick. Cheek almost wholly covered by the subor- 

 bitars. Each nostril with two oi)enings, the anterior one a project- 

 ing tube like a barbel, the posterior one an aperture near the eye. 

 Upper arch of the mouth formed by small premaxillaries and large 

 moveable maxillaries. Teeth on the jaws ; vomer, pterygoids, pala- 

 tines, and large double branches of the mandible, mostly in rows 

 of conical teeth, with small tesselated patches behind ; on the pha- 

 ryngeals the teeth are cardiform, and rough granular patches exist 

 on the internal face of the operculum, a singular piece of structure 

 which M. Valenciennes regards as the rudiment of an accessory bran- 

 chia. The tongue is edentate, thick and fleshy. Large gill-openings. 

 Branchiostegals eleven to twelve ; broad and flat. Scales of the 

 body thick, butnot osseous. Caudal coming farther forward on the 

 upper edge of the tail than below; ventrals median ; dorsal long; 

 anal small. Stomach caecal, with a large pyloric valve. No pan- 

 creatic caeca; a very large air-bladder, forking anteriorly, and 

 communicating with the cesophagus ; cellular within, in the upper 

 and lateral parts, but not below. Ova dropping into the cavity of 

 the abdomen. Fresh waters of America. Ten species. 



Family IV.— STURIONID.E. 



Sturiones, Sturioniens ou Chondropterygiens, abranchies Uhres, Cuv. 

 Chondrostei, JliiU. ; Accipenserini, Miill. ; Acdpenseridce, Bonap. 

 Skeleton partly cartilaginous, vertebraJ column a soft chorda in- 

 stead of vertebra;. 



Genus I. Accipenser, Linn. Form squaloid. Bod 

 less protected by rows of bonj shields. Head cuir^ 

 beneath the snout, small and toothless. The premaxil 

 anterior inferior border of the upper jaw; tlie maxjy 

 oblong plate articulated to the outer process of the^ii 

 and by the whole of its inner posterior side to the palatine bone. 

 The mandible consists principally of a single bony limb, which is 

 joined to its fellow at the symphysis, and its joint is formed by 

 a trochlear cartilage attached to the pterygoid process of the pala- 

 tine. The mouth thus formed is more protractile than that of the 

 Sharks. Kostral barbels on the ventral aspect. Labyrinth in form 

 and position resembling that of the osseous fishes. No vestige of an 

 external auditory opening. An aperture behind the temples con- 

 ducts merely to the gills. Dorsal and anal opposite, behind the 

 ventrals; caudal encircling the extremity of the spinal column, 

 the upper lobe the principal one, a smaller and shorter one be- 

 neath. Spiral intestinal valve, and conglomerated pancreas as in 

 the Shark.s ; a very large swim-bladder communicating with the 

 oesophagus by a large hole. 



Genus II. Polyodon, Lacep. Spatularia, Shaw. Planirostra. 

 Scaphirhynchus. Technically distinguished from Accipenser by the 

 naked skin destitute of bony shields ; recognisable at once by the 

 enormous leaf-like expansion of the snout. In general form Stur- 

 geons, but the gill-openings are larger, and the membninous tip of 

 the gill-flap reaches the middle of the body. Jlouth very wide, with 

 a multitude of little teeth. A gelatinous chord in the spine like 

 that of the Lamprey. A spiral intestinal valve ; pancreas par- 

 tially divided into ca^ca ; an air-bladiler. Miiller says that the 

 opercula are absent in Polyodon. (Osteol. der Myxin.) 



