224 REPORT OF NEW JERSEY STATE MUSEUM. 
dorsal, with a single spine. Pectorals rather short, unusually 
far behind gill-openings. Caudal narrow, usually emarginate. 
Ventral fins sub-abdominal, consisting of a stout spine and 1 or 
2 rudmnentary rays. . 
Small fishes of the fresh waters and the arms of the seas in 
northern regions. Noted for their pugnacity, exceedingly de- 
structive to the spawn and fry of larger fishes. Most build elab- 
orate nests, which the male defends with spirit. They are ex- 
tremely variable and are apparently readily affected by changes. 
in their surroundings. 
Key to the genera. 
a, GASTEROSTEIN. Pubic bones fully joined, forming a triangular or lan- 
ceolate plate on median line of belly behind and between ventrals. 
b. Gill-openings confluent, membranes forming a broad free margin across. 
isthmus; dorsal spines VIII to XI, divergent; skin naked or nearly 
so. PYGOSTEUS. 
bb. Gill-openings restricted, membranes mesially united to isthmus; dorsal 
spines XI, free; skin mailed, partly mailed, or naked. GASTEROSTEUS 
aa. APELTIN2. Pubic bones widely separated posteriorly, forming a bony 
ridge on each side of abdomen between which are ventral fins; dorsal 
spines IV, divergent; sides not mailed. APELTES. 
Genus Pycostreus Gill. 
The Nine Spined Sticklebacks. 
Pygosteus pungitius (Linnzus). 
Ten Spined Stickleback. Many Spined Stickleback. 
Stickleback. 
Head 3%; depth 5%; D. X, I, 9; A. I, 10;\length of caudal 
peduncle 124 in head; length of caudal 144; pectoral 134; ven- 
tral spine 2%; snout 3% in head, measured from tip of upper 
jaw; eye 344; maxillary 3%; interorbital space 444. Body very 
slender, compressed, and tapering into long, slender caudal 
peduncle, which is strongly keeled, broader than deep, and much 
depressed. Head compressed, rather attenuate, and upper profile 
sloping a little more than lower. Snout rather conic. Eye 
