178 
Journal of the Mitchell Society [December 
KEY TO THE CLASSES OF FISHES AND FISH-LIKE ANIMALS 
i. Animals with cartilaginous skeleton and without brain 
or skull; fins rudimentary and only on median line of body; 
mouth a slit surrounded by bristles; heart a tubular vessel 
without separate chambers; blood colorless; gillslits 
numerous, the respiratory cavity opening into the abdomen; 
inspired water discharged through a special abdominal pore. 
leptocardii (lancelets). 
ii. Animals with cartilaginous or bony skeleton; skull and 
brain present; heart developed as a cavity with at least two 
chambers; blood red. 
a . Eel-shaped; skeleton cartilaginous; skull imperfect; 
mouth circular, suctorial; no jaws or paired fins; a 
single median nostril; gills pouch-shaped and numerous; 
skin naked; alimentary canal straight, without coeca; 
pancreas and spleen absent. 
Marsipobranchii (lampreys, etc.) 
aa. Skull well-developed; jaws distinct; fins usually 
highly-developed, some of them paired; skin usually 
scaly; nostrils at least two, not median; gill-openings a 
single slit on each side in most fishes (numerous in a 
few families); alimentary canal more or less convoluted; 
pancreas and spleen present. 
Pisces (fishes). 
Of the third class, Pisces, the North Carolina representa- 
tives fall into two easily recognized groups or sub-classes: 
(1) the Shark, Skates and Rays and (2) the True Fishes, 
which are distinguished anatomically as follows: 
i. Skeleton cartilaginous; skull without sutures and with- 
out membranous bones; gill openings numerous (5 to 7) and 
slit like, the gills attached to the skin; tail heterocercal; skin 
tough, naked or covered with small rough scales, spines, or 
tubercles; air-bladder absent; jaws separable from skull; 
species viviparous or ovoviviparous, the eggs large and few 
in number; embryo with deciduous external gills. 
Selachii or Elasmobranchii (sharks, skates, rays, etc.) 
