The Anatomy of Chlamydoselachus 345 



between a scale and a tooth in Chlamydoselachus is that the scale has but one projection 

 large enough to be called a spine, while the tooth usually has three large spines or cusps, 

 and two rudimentary cusps. The question arises: does a single scale correspond to an 

 entire tooth, or does a tooth develop as an aggregate of several scale^like rudiments? 



Near the angles of the mouth of Chlamydoselachus, teeth sometimes grade into 

 scales. In the four large specimens studied by Gudger and Smith (1933), the teeth of the 

 last rows, as these approach the angles ot the jaws, become very small, irregular and 

 rudimentary until finally it is with great difficulty, even with the aid of a strong lens, 

 that rows of teeth can be distinguished from groups of undoubted scales like those shown 

 in Text-figure 10. The teeth are not comparable to individual scales, but each cusp 



Text-figure 10. 

 Placoid scales or dermal denticles 

 (x 5) from the angle of the mouth of 

 Chlamydoselachus. Each scale re- 

 sembles a single cusp of the rudimen- 

 tary three-cusped teeth occurring in 

 this region. 

 After Garman, 1885.2, Fig. 12, pi. VI. 



resembles a scale, and the scales are sometimes arranged in columns of threes in series 

 with the rows of teeth. In two specimens the border line between teeth and scales 

 could be distinguished with considerable certainty, but in the other two specimens there 

 was room for doubt. On the other hand, Garman (1885.2, p. 5) says of his single adult 

 specimen: "the change from teeth with broad base, three cusps, and two buttons [rudi- 

 mentary cusps] is sudden and decided; i.e., they do not grade into each other. A strong 

 lens, however, is necessary to distinguish them, since in the hinder row each cusp looks 

 much like a single scale." The last statement, together with the observations of Gudger 

 and Smith, suggests a multiple origin for each tooth. 



The development of a placoid scale has not been studied in Chlamydoselachus; but 

 in the leopard shark, Tria}{is semifasciatus, a scale develops from a single primordium 

 (Daniel, 1934, p. 26 and Fig. 29). It is of interest to inquire whether the multicusped 

 teeth of Chlamydoselachus develop in the same manner. 



The teeth of a 340 mm. embryo of Chlamydoselachus have been studied by Rose 

 (1895). In this embryo, none of the teeth (Text-figure 11) had attained its final form, but 

 some in the middle of each row were like those of the adult except that they lacked the 

 two very small cusps. The innermost teeth of each row were represented, individually, 

 by three distinct cusps not yet united at their bases; apparently each cusp had developed 

 from a separate primordium. The evidence certainly indicates that, at the inner end of 



