FISHERY BULLETIN; VOL. 76. NO. 3 



KEY TO THE SPECIES OF 

 THE GENUS DIODON 



la Two or more small spines wholly on the dorsal or dorsolateral surfaces of the caudal 

 peduncle (Figure 2A); color pattern of adults dominated by small (smaller than eye) 

 spots; at least D, P, and C fins of adults with dark spots 2 



lb No spines w^holly on the caudal peduncle (Figure 2B); color pattern of adults dominated 

 by large dorsal and lateral bars or blotches; fins of adults without spots except in some 

 cases at base 3 



2a P 19-22. both D and A 16-18; D and A of adults falcate; S-A spines^U; head width less 



than 30'y SL D. eydouxii 



(circumtropical, oceanic) 

 2b P 22-25 (rarely 21), D 14-17, A 14-16; D and A of adults rounded; S-A spines&14; head 



width greater than 307^ SL D. hystrix 



(circumtropical, shore fish but juveniles pelagic) 



3a No small, fixed, tribase spine immediately above the gill opening; no small, flat spines on 

 the anterior border of the depression surrounding the gill opening (Figure 4); S-A spines 

 ^11; adult color pattern dominated by four large lateral bars, dorsum uniformly 



dark D. nicthemerus 



(Australia) 



Figure 4. — Head of Dwdon nicthemerus (AMS 1.16990-004) showing arrangement of spines in 

 the region of the gill opening. Note that spines anterior to gill opening are not flattened. Also note 

 tubular nostril. 



3b One or two small, fixed, tribase spines above the gill opening; three or four small, flat 

 spines forming the anterior border of the depression surrounding the gill opening ( Figure 

 5); S-A spines S3l2; adult color pattern dominated by several dorsal blotches 



540 



