102 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. VII. 



HEAD is measured from tip or upper jaw to the posterior edge of the 

 opercle; the LENGTH of the SNOUT, from tip of upper jaw to anterior 

 margin of the orbit. The DEPTH of the BODY is measured at its 

 deepest part, none of the fins being included; the DEPTH of CAUDAL 

 PEDUNCLE is measured at its narrowest part, its length from base of 

 last anal ray to end of last vertebra. 



The SCALES in the LATERAL SERIES are counted from upper edge 

 of opercle to base of caudal fin, the TRANSVERSE SERIES from the dor- 

 sal fin to ventrals or origin of anal, whichever is nearest the middle of* 

 the body. In making the transverse count the scale on the lateral 

 line, when it is present, is counted with those on the upper part of 

 the body. The LENGTH of the DORSAL and ANAL FINS is measured 

 along their BASES; the HEIGHT is the length of their spines or rays. 

 The length of the other fins is measured from attachment to the 

 body to the tips of the longest rays. 



In order to abbreviate, the following expressions are used: " HEAD 

 4" indicates that the head of the fish is contained 4 times in the 

 distance from the tip of the snout to the end of the last caudal verte- 

 bra ; "DEPTH 4 " that the greatest depth (none of the fins being included) 

 is contained 4 times in the same distance; "D. 8" indicates that the 

 fish has a single dorsal fin which is composed of 8 soft rays; "D. iv, 

 9," that the dorsal fin is single and is composed of 4 spines and 9 

 soft rays; "D. iv-g," that there are two dorsal fins, the first one 

 composed of 4 spines and the other of 9 soft rays. Spines are 

 always indicated in roman letters, soft rays by figures. The abbrevi- 

 ations used in the count of other fin rays and spines are similarly 

 explained. The diameter of the eye, the length of the snout, and 

 many other short measurements are compared with the length of 

 the head. "Eye 3 in head," "Snout 3 in head," indicate that each 

 is contained 3 times in the length of the head. In these particular 

 cases " J/s of the length of head" would mean the same thing. 



KEY TO THE FAMILIES OF FISHES OF THE GREAT LAKES 

 OF NICARAGUA. 



a. Gill openings slit-like, 5 in number, on each side. 



b. Gill openings lateral; no spiracles; snout not produced into 



a long flat blade. Galeidce 103 



bb. Gill openings ventral; spiracles present; snout produced into 

 a long, thin, flat blade, armed with teeth along each edge. 



Pristida 104 



