590 PROCEEDINGS OF THE NATIONAL MUSEUM vol. lu 



Rhizoprionodon Whitley 



Rhizoprion Ogilby, 1915, Mem. Queensland Mus., vol. 3, p. 132 (type Carcharias 

 (Scoliodon) crenidens Klunzinger, 1880, a synonym of Carcharias acuius 

 Riippell, 1835, by original designation), a junior homonym of Rhizoprion 

 Jourdan, 1861, a fossil Cetacean. 



Rhizoprionodon Whitley, 1929, Australian Zool., vol. 5, p. 354 (a substitute 

 name for Rhizoprion Ogilby). 



Protozygaena Whitley, 1940, The fishes of Australia, vol. 1, p. 110 (type Physodon 

 taylori Ogilby, 1915, by original designation; retained in my study as a 

 subgenus). 



Diagnosis. — Sharks of small to moderate size (reaching a t.l, of 

 at least 1000 mm.) distinguished from other carcharhinid genera by the 

 following combination of characters: origin of second dorsal fin ranges 

 from over middle of anal base (rarely) to over anal axil; cusps of teeth 

 smooth to serrulate and obliquely directed rearward; labial furrow on 

 upper jaw usually well developed, except in most specimens of R. 

 oligolinx and R. taylori; lower labial furrow visible when mouth is 

 closed; pectoral fin origin below fourth to third gill-opening; tip of 

 posterior margin of first dorsal fin not reaching much, if any, beyond 

 level of pelvic origin ; distal tip of appressed pectoral fin not extending 

 posteriorly much, if any, past level of anterior two-thirds of first dorsal 

 base; differing from all carcharhinids I have examined in having a 

 discrete series (sometimes irregularly biserial) of enlarged hyomandib- 

 ular pores on the outer side of each corner of the mouth. Other 

 distinguishing characters as in key couplets lb and 2b (p. 568). 



Subgenera. — I recognize two subgenera, Rhizoprionodon and 

 Protozygaena, within the genus. The nominal subgenus includes R. 

 terraenovae, R. porosus, R. acutus, and R. longurio; the subgenus 

 Protozygaena includes R. lalandei, R. taylori, and R. oligolinx. 



The nominal subgenus differs from Protozygaena in having markedly 

 elongate centra in the posterior monospondylous region (plate 2a), 

 as opposed to scarcely elongate centra in that region (plate 2b, c); 

 in only rarely having more precaudal vertebrae than caudal vertebrae, 

 as opposed to always having more precaudal than caudal vertebrae 

 in Protozygaena; in the absence of a marked sexual dimorphism of the 

 dentition of the lower jaw of adults, as opposed to its presence in 

 Protozygaena; in having the cusps of at least some teeth noticeably 

 serrulate in large specimens, as opposed to smooth or faintly irregular 

 cusps in Protozygaena; in generally having more teeth, a longer upper 

 labial furrow, in attaining a size of 900-1000 mm., and in having males 

 mature only at sizes greater than 600 mm., as opposed to fewer teeth, 

 a shorter upper labial furrow, in attaining a size of less than 700 mm., 

 and in having males mature at less than 600 mm. (as small as 380 

 mm. in R. oligolinx). 



