674 Bashford Dean Memorial Volume 



McCoy's descriptions and drawings (1890) of the teeth of H. phillipi (my Text-figure 

 14) are excellent. "Teeth alike in both jaws, the median tront rows very small, acutely 

 tricuspid when young, simple and ■w.'ith obtusely triangular cusp in middle age, blunt and 

 hexagonal when old: more posterior teeth large, oblong, longer than broad, flattened, 

 arranged in oblique, spiral row-s on each side ot the jaw, the anterior and posterior ones 

 smaller than those in the middle."" His figure of the lower jaw (my Text-figure 14bj 

 reveals a distinct longitudinal ridge on each of the posterior grinding teeth — a feature 

 mentioned but not figured by Maclay (1879). The lower jaw shows a distinct line of 

 demarcation between anterior cusped teeth and posterior grinding teeth — as in the 

 figure by Phillip (Text-figure 10) but not to the same degree. In this jaw there are only 

 eleven transverse rows of anterior cusped teeth. These, w^th eight rows, on each side, of 

 posterior grinding teeth, make a total of 27 rows in this lower jaw. Text-figures 14a 

 and 14c show, respectively, the appearance of the mouth when it is closed and when it is 

 open. The lower jaw^ in Text-figure 14c is identical with that in Text-figure 14b. The 

 upper jaw, shown in Text-figure 14c, likewise has 27 row^s of teeth. Of these, 12 or 13 

 rows are anterior or cuspidate teeth. The transition between cuspidate and grinding 

 teeth is not so abrupt as it is in the lower jaw. 



Carman (1913, Figs. 4 to 6, pi. 47) portrays the teeth of a male Heterodontus phillipi 

 about 864 mm. (34 inches) long. The transition between anterior (cuspidate) and posterior 

 (^grinding; teeth is not so abrupt, in this specimen, as in some others. The dividing lines 

 here chosen are somewhat arbitrary. The upper jaw has 13 transverse rows of anterior 

 (cuspidate) teeth and 10 rows (5 on each side 1 of posterior (grinding) teeth, making a total 

 of 23 rows. The lower jaw has 11 rows of anterior (cuspidate) teeth and 8 rows (4 on 

 each side) of posterior (grinding) teeth, making a total of only 19 rows. Carman"s figures 

 of the posterior grinding teeth or "molars"" show on each tooth a distinct longitudinal 

 ridge or ""keel"", and on each side of this, many fine transverse ridges. Carman states that 

 the ridges on the molars of younger specimens become less conspicuous w^th age and use, 

 and that the harder the food in a particular locality the fainter the ridges appear. 



To summarize the recorded data on the dentition of the adult or nearly adult Hetero- 

 dontus philUpi, one may sute that all the descriptions and drawings emphasi2;e the decided 

 differences between anterior and posterior teeth — differences that suggested the generic 

 name, Heterodontus. When we compare the dentition of upper and lower jaws, we find 

 that Bridge's statement "dentition similar on both jaw^s'' is true of all specimens that have 

 been described. One may be more definite and explain that the dentition (meaning the 

 kind, number and arrangement of the teeth ) is aHke on upper and lower jaws, with certain 

 slight reservations. First, as McCoy states, there are usually "a few more rows in upper 

 than [in] lower jaw"". Using the meager data available we find that the average number of 

 transverse rows on the upper jaw (6 cases, average 31.0 rows) is slightly greater than 

 on the lower jaw (6 cases, average 28.8 rows). In only one instance (McCoy's drawing) is 

 the number of rows of teeth the same on both jaws. The largest number of teeth recorded 



