74 CONTRIBUTIONS TO NORTH AMERICAN ICHTHYOLOGY IV. 
aa. Arterial bulb with a pair of opposite valves; optic nerves not foriniug a cbiasraa. 
(Series Teleostei.^) 
c. Air-bladder (if present) connected by an air-dnct with the stomach or 
cesopliagus ; ventral fins (if iiresent) abdominal, their basilar segments 
riidimental, nsually •without sjiines ; parietal bones usually united. 
PlIYSOSTOMI. 
cc. Air-bladder •without duct ; ventral fins (if present) usually thoracic or 
jugular, without basilar segments ; spines usually present, at least in the 
dorsal and ventral fins ; parietal bones separated by the 8upraoccii)ital. 
PllYSOCLISTI. 
AIITIFICIAL KEY TO THE FAMILIES OF PISCES. 
The follo^Yillg key is intended simply to facilitate tlie identification of 
species. Ko attempt is made to indicate the natural ckaracters or rela- 
tions of tke families, and only those species of any group which occur 
within the limits of the United States are taken into consideration. 
I.— VENTRAL FINS PRESENT, ABDOMINAL. 
* Dorsal fins 2, the anterior chiefly of soft rays, the posterior adpiose. 
A. Body naked. 
B. Head with 4 to 8 long barbels ; dorsal and pectoral fins each with a spine. 
SiLURiDJi;, 29. 
BB. Head without barbels ; fins without spines. 
C. Teeth strong; dorsal fin many-rayed AEEPiDOSAURiDiE, 40. 
CC. Teeth minute; dorsal fin short Steeyoptyciildas, 43. 
AA. Body scaly. 
D. Teeth broad, incisor-like Ciiap.acinid^, 32. 
DD. Teeth (if present) pointed. 
E. Margin of uiiper jaw formed by the premaxillaries alone. 
F. Dorsal fin nearly median. 
G. Body wTtli phosphorescent spots ScoPELiDiE, 42. 
GG. Body without xrhosphorescent spots. 
H. Head scaly ; scales cycloid ; teeth cardiform ScoPELiDiE, 42. 
HH. Head naked; scales ctenoid ; teeth villiform.-PEP.coPSiDAi;, 47. 
FF. Dorsal fin x)osterior; teeth unequal ; body elongate. . Paralepid.^,41. 
EE. Margin of upper jaw formed by maxillaries posteriorly. 
J. Body with phosphorescent spots; gill-rakers none. 
CnAULIODOXTID.E, 44. 
JJ. Body without ]>hosphorescent spots; gill-rakers present. 
SALMOXIDJ3, 46. 
** Dorsal fin single, preceded by free spines. 
Iv. Body scaleless, naked or with bony plates. 
L. Ventral fins I, 1, the sirine strong; snout moderate. 
GASTEROSTEIDiE, 64. 
LL. Ventral fins I, 5, the spine slender; snout xirolonged. 
AULORIIA'XCniDiE, 63. 
KK. Body scaly; .snout tubular AuLOSTOMAXioiE, 62. 
rt’/leof, perfect ; oGTeov, bone. 
