The Embryology of Heterodontus japonicus 679 



In my 527'mm. female specimen of H. quoyi, the entire supraorbital ridge is low, but 

 it is lowest in its middle third where it is a mere fold of skin, not supported by the endo' 

 skeleton. This fold overlaps the eyeball like an upper eyelid. Its function is doubtless 

 protection of the eye while the fish is forcing its way under rocks or into crevices. When 

 pressed upon, this fold of the skin reduces the palpebral fissure to a narrow slit. Though 

 in all species of Heterodontus the supraorbital ridge leans outward, thereby overhanging 

 the eye, H. quoyi is probably the only species in which any part of it actually overlaps the 

 eyeball. In my adult female specimen of H. quoyi the supraorbital ridge does not end 

 abruptly, as it does in H. francisci. 



In the same adult female specimen of H. quoyi, the "cheeks" appear swollen, and the 

 gill'covers, especially the first, bulge outward as if inflated by pressure from within. It 

 seems hardly likely that this condition could be produced by unequal shrinkage, since 

 it does not occur in other specimens preserved in the same way. As viewed from above, 

 the head is broad behind and somewhat pointed in front, like the head of a venomous 

 snake. The ventral surface of the head is decidedly flat, and lies in the same plane as the 

 ventral surface of the body. The nasal apertures open ventrad. As viewed from the side, 

 the dorsal surface of the head slopes forward to a fairly sharp rostrum directly in front 

 of the nostrils. The dorsal fins are small. The hind margin of the first dorsal is slightly 

 convex, that of the second dorsal is almost straight. The dorsal spines are decidedly small 

 but are much worn ; they project less than a centimeter beyond the skin. The pectoral fins 

 are broad and when extended (as far as possible in their rigid condition) the distance from 

 tip to tip is about 250 mm., equal to nearly half the body length. The scales on the 

 ventral surface of the body are smooth ; those on the dorsal surface are tuberculate and 

 are much larger than the scales on the ventral surface. 



The form of my young specimen of H. quoyi (a male 372 mm. long) differs considerably 

 from that of the adult specimen (a female). Both head and body are more slender, especial' 

 ly in width. The ventral surface of the head is not so flat as in the adult. The supra' 

 orbital ridges are taller proportionally; they are especially well developed at their posterior 

 ends, where they terminate abruptly. Though the middle portion of each supraorbital 

 ridge is depressed, it overhangs the eye much less than in the adult. The dorsal fins are 

 proportionally larger, and the spines longer and sharper, than in the adult. The posterior 

 edges of both dorsals are so frayed that the original shapes of their margins cannot be 

 determined. It seems unHkely that any of the differences noted are due to sex. Some 

 characters, like the abrupt termination of the supraorbital ridges, may be individual vari' 

 ations, but most of the differences are probably correlated with differences in age. 



In my two specimens of H. quoyi, the entire body, including the fins, is ornamented 

 with many dark'brown (nearly black) spots of various sizes. Of these, few are larger 

 than the orbit. These spots are occasionally grouped in twos, threes and fours. On the 

 dorsal surface there is a fairly regular bilateral arrangement of spots or groups of spots, 

 though in the large female the spots on that surface are more or less obscured by a dark' 

 brown ground color. On the ventral and ventrolateral surfaces the distribution is 



