12 PISCES. 



Class E. — PISCES. (The Fishes.) 



A " fish " in tlic popular Fcnso is a member of any one of the 

 three classes of a<iiiatic or fish-like vertebrates, the groujis here 

 designated as Leptncardli, Mdisi/xihranr/iii, and Pi.'ices. lint the 

 Lnnct'lrls and the Lnmprri/s differ so widely from the other groups 

 that we must exclude them from consideration as fishes. Many 

 writers go still further and remove from the PL<<ces, the SliarkSf 

 Chimaras, and Dlpnoans, but for our present purposes all these 

 may be referred to the same class as the true fishes, or T< hosts. 

 The Piscex or " Fishes " may then be defined as cold-blooded ver- 

 tebrates adapted for life in the water, breathing by means of gills 

 which are not purse-shaped, but attached to bony or cartilaginous 

 gill arches ; having the skull well developed and with a lower jaw ; 

 with the lind)s present and develojx'd as fins, or rarely wanting 

 through atrophy ; with shouliler girdle present, furcula-shaped, 

 curved forward and with the sides connected below ; with pelvic 

 bones present ; having the cxoskeleton developed as scales or bony 

 plates or horny appendages, sometimes obsolete, and with the me- 

 dian line of body with one or more fins composed of cartilaginous 

 rays connected by membrane. The existing representatives of the 

 class Pisces may be conveniently divided into four subclasses : 

 Selachii or Klasmohrnnchii, Jfolncephali, Tclcnstnini, and Dipuni. 

 The last group {Ceralmlus, Lrpidosiren) has well-developed lungs 

 and the paired fins fiipper-like. It forms a conne<'ting link be- 

 tween the GnnoHi'i and the Bntrarhia. As there are no North 

 American s[)ecies of Dipnoi, the group needs no further men- 

 tion in this work. 



Subclasses of Pisces. 



o. Gills not freo, bcinfj attarhcd to the skin by the outer marpin. Ova few 

 anil hir^c, iinprei;iinted and sometimes developed infernally: emlirvo 

 with deciduous external frills ; membrane bones of head undeveIo|>«'i|. 

 except sometimes a rudimentary opercle; skeleton rartilauinous; skull 

 without sutures; tail heterorerca! ; ventral tins abdominal: male with 

 larfce intmmitlent organs or claspers attached to ventral fins; skin 

 naked or covered with minute roupth scales, sometimes with spines; no 

 air-bladder; arterial bulb with three series of valves; intestine with a 

 spiral valve; optic nerves united by a chiasma; cerebral hemispheres 

 united. 

 b. Gill op«'ninps slit-like, 5 to 7 in number; jaws distinct from the skull, 



joined to it by suspensory bones; no membrane btmes; teeth distinct. 



{Sharh and Skattt.) Sf.i.achii, page 14. 



