662 Bashford Dean Memorial Volume 



jaws of Heterodontus is hyostylic, but with a very extensive articulation of the palatO' 

 quadrate with the cranium, so that the hyomandibular scarcely acts as a real support 

 (my Text'figure 33, page 700). The suspension of the jaws is further discussed on pages 

 699 to 701 of the present article. 



Carman's definition (1913) of the family Heterodontidae (his Centraciontidae) 

 attempts to separate family characters from generic ones; but since he excludes fossils, the 

 description really applies to only one genus, Heterodontus. Carman vvorites: 



The Hving species of this family are small sharks which have short bodies and heads, 

 blunt snouts, small spiracles below the hinder part of the eye, a narrow mouth near the end of 

 the snout, with about four lobes in each half of the upper Hp, both cuspidate teeth and grind' 

 ers, five gill-openings of which several are above the pectorals, eyes without nictitating 

 membranes or folds, nostrils connected with the mouth by naso-oral grooves, without cirri, two 

 dorsals each preceded by a strong rigid spine, an anal behind the second dorsal, a short deep 

 caudal, small carinate scales, a preorbital articulation between upper jaw and skull, and 

 asterospondylous vertebrae. 



In the phrase "eyes without nictitating membranes or folds", it is not quite clear 

 what Carman means by the word "folds". If he means a fold of ordinary skin, then my 

 adult specimen of H. quoyi is an exception, for it possesses a fold of skin capable of over- 

 lapping the eye somewhat like an upper eyelid. 



The genus Heterodontus, which Carman calls Centracion, is characteri2;ed by him 

 (1913) as follows: 



Head short, snout blunt, crown narrowed, between strong orbital ridges. Eyes small, 

 lateral. Nostrils with two thick valves reaching the mouth and curving toward the grooves. 

 No narial cirri. Mouth narrow, with thick labial folds on both jaws. Teeth alike in upper 

 and lower jaws, cuspidate in the anterior series, elongate longitudinally ridged grinders 

 posteriorly. Pectorals large, dorsals moderate, anal small, caudal short. 



The present writer has not been able to examine specimens of all species of Hetero' 

 dontus, but the evidence at hand indicates that unusual breadth of the head and anterior 

 part of the body, and decided flatness of the ventral surfaces of both head and body, are 

 typical for adult specimens of this genus. A slightly humpbacked appearance, observed in 

 my specimens of H. quoyi and H. jrancisci, is possibly a generic or even a family character. 

 The supraorbital ridge leans outward, overhanging the eye. The anterior teeth are 

 quincuspid in the very young; and acutely tricuspid in older specimens, with the median 

 cusp increasingly predominant. In the adult they are often simple, becoming blunt 

 when old. The lips, nasal apertures and naso-oral grooves of a single specimen of Hetero' 

 dontus, probably jrancisci, have been described in detail by Allis (1919, pp. 158-164 and 

 Figs. 6 and 7, pi- I- 



A vestigial sixth branchial arch was found by Hawkes (1905) in two species of 

 Heterodontus — phillipi and jrancisci. The other species were not available for exami- 

 nation. Hawkes states that the presence of a rudimentary sixth branchial arch in Hetero^ 

 dontus is in harmony with the view that the Heterodontidae are in some respects inter- 



