The Anatomy of Chlamydoselachus 



343 



and Smith (1933). We are here concerned chiefly with the structural and developmental 

 relations between scales and teeth. The latter are not ordinarily considered as external 

 structures, but are discussed here because of their morphological relationship to scales. 



Some typical scales of Chlamydoselachus are shown in Text'figure 6. Each scale is, 

 essentially, a hollow cone with ridges extending from the base to the apex. It is composed 

 of dentine covered with a thin layer of enamel. In addition to the single prominent 

 spine there are sometimes, as shown in Text-figure 6a, slight elevations near the margin 

 of the base, formed by intersecting ridges. These elevations might easily develop into 



Text-figure 6. 

 Three different views of a placoid scale or dermal denticle (x 130) from a 340-mm. embryo of Chlamy- 

 doselachus: A, scale from the flank, viewed from above; B, lateral view of a scale from the region of 

 the tail; C, scale from the region of the tail, seen from beneath. 

 After Rose, 1895, Abb. 1, 2, 3. 



accessory spines. Of the atypical scales, those forming the "armature" on the anterior 

 edge of the dorsal fin (Garman, 1885.2, p. 7; Gudger and Smith, 1933, p. 294) are interest- 

 ing because, in form and arrangement, they resemble the "fulcral scales" of the Actin- 

 opterygii. The latter are described by Goodrich (1909, p. 304), and are said to be quite 

 peculiar to this group. 



A typical tooth, viewed from three aspects, is represented in Text-figure 7- It 

 has three sharp, slender, curved cusps, and two rudimentary cusps or denticles. It is 

 attached to the jaw in such fashion that the denticles project inward toward the mouth 

 cavity. The broad base of the tooth is prolonged posteriorly (toward the interior of the 

 mouth) and is forked so as to interlock with a paired excavation in the base of the suc- 

 ceeding tooth. In the illustrations the prongs of the base might readily be mistaken for 

 cusps, but in the actual specimens the appearance is very different since the base is com- 

 posed entirely of dentine while the cusps are covered with shiny white enamel, 



