FISHES OF CHESAPEAKE BAY 
33 
USE OF KEYS 
The keys have not been made with the view of showing natural relationships, 
but they are intended purely for the purpose of ready identification, and in preparing 
them only the characters applicable to the fishes of Chesapeake Bay have been taken 
into consideration. In using the keys, first determine to which of the major groups 
-TOTAL LENGTH 
VENTRAL FIN 
LIMING GiLL^CAVITY 
/<7\ /UPPER 
ARCH 
ARCH^ 
GILL 7 RAKERS X GiLL3 
Fig. 24. — Diagram of a sciffinid, explaining terms used in keys and descriptions 
the specimen in hand belongs; then take up the regular order of letters under that 
group. If the characters of the specimen do not agree with those under the single 
letters, look under the double letters (occasionally triple letters are used), ignoring 
all intervening matter. By means of indentations, the order of subordination of the 
minor groups to the major groups is shown. 
KEY TO THE FAMILIES 
I. LEPTOCARDII: Amphioxi (the lancelets). — Skeleton a cartilaginous rod; brain and skull 
wanting; body elongate, compressed, translucent; mouth a longitudinal slit, surrounded by 
cirri; eyes and fin’s rudimentary Branchiostomidx (lancelets), p. 42 
II. M ARSIPOBRAN CHII : Hyperoartia (the lampreys). — Skeleton cartilaginous; brain and 
skull present; body eel-shaped; head not differentiated from the body; mouth circular, 
suctorial; seven small, round gill openings on each side Petromyzonidse (lampreys), p. 43 
