The Anatomy of Chlamydoselachus 



347 



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Text-figure 13. 

 Placoid scales from two species of the Devonian shark Cladoselache. 



A — Scales (x 25) from various parts of the body of C. fyleri. From a specimen in 



the American Museum. 

 B — Trifid scale (x 20) from near margin of mouth of C fyleri. From a specimen in 



the American Museum. 

 C — Larger scales (x 10) of Cladoselache (probably clarl^). From a specimen in the 



British Museum. 

 After Dean, 1909, Figs. 1, 2, 3. 



In Chlamydoselachus and in Heptanchus (Daniel, 1934, Fig. 27) the structure of the 

 scales is simple and conforms to the same fundamental plan, though in both fishes the 

 form of the scales varies considerably on different parts of the body. One should not 

 attribute much phylogenetic importance to differences in the form of the scales of elas' 

 mobranchs. Some of the most specialized elasmobranchs (e.g., Raja) have simple scales, 

 while the fossil Cladoselache, one of the most primitive sharks, has scales of various 

 forms ranging from those only slightly indented or subdivided (Text'figures 13a and b) 

 to those indented to such a degree that their exposed surfaces bristle with cusp'like 

 points or ridges (Text-figure 13c.) In Cladoselache as in modern sharks, the scales vary 

 in size and shape in different regions of the body (Dean, 1909, p. 214). 



The teeth of Chlamydoselachus are 

 barb-like, prehensile. In Heptanchus 

 (Text-figure 14) the teeth are not alike on 

 upper and lower jaws. The upper teeth 

 seem adapted mainly for holding, the lower 

 ones for cutting. The decided differences 

 between the teeth of Chlamydoselachus 

 and Heptanchus — forms which, in many 

 important respects, seem closely related — 

 serve to weaken one's faith in the validity 



Text-figure 14. 



Dentition of Heptanchus (AJotidanus) indicus. 



a, teeth in function; fa, teeth in reserve; u and I, upper and 



lower single teeth (natural size). 



From Goodrich, 1909, after Giinther, 



