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Bashford Dean Memorial Volume 



each row, teeth were being formed by the 

 union of simple denticles homologous with 

 placoid scales. At the outer ends of the 

 rows, the teeth were small and rudimentary; 

 each tooth had from one to three cusps. 

 Those with a single cusp bore a strong resem' 

 blance to placoid scales. In the teeth with 

 two or three cusps, the cusps were so closely 

 fused at their bases that the enamel was con- 

 tinuous from one cusp to another. According 

 to Rose, these teeth represent a stage transi' 

 tional to the adult teeth of many teleosts. 

 Possibly these teeth were anomalous, since in 

 my four large specimens the outer teeth are 

 only slightly different from those at the middle 

 of each row: all have three cusps well devel' 

 oped and well separated. Rose thinks that all 

 the two' and three-cusped teeth of his embryo 

 developed through the fusion of simple cusps. 

 On one side of the upper jaw of his em- 

 Teeth of the lower jaw (x 5) of a 340-mm. embryo ^ R5se found the first two teeth of the 



of Chlamydoselax:nus, in their natural positions. i . i • i i • i i i i- ■ i 



. , „ third row united at their bases, but delimited 



After Rose, 1895, Abb. 5. , , yr^ r r • x ^ 



by a deep groove (Text 'figure 12 herein). One 

 of these teeth has but one cusp, the other has two cusps. Rose claims that this 

 anomaly has a phylogenetic significance, since it indicates the manner in which a jawbone 

 might arise through the fusion of teeth at their bases. Further, Rose asserts that the 

 three- and especially the five-cusped teeth of an adult Chlamydoselachus furnish an 

 excellent transition between a single-cusped shark tooth and the toothplates of an adult 

 Siren, likewise of all urodele embryos. Also, he finds in his Chlamydoselachus embryo 

 all possible forms intermediate between a simple placoid scale and a three-cusped tooth. 

 The single-cusped tooth shown at the left in Text-figure 12 differs very little from a simple 

 scale and is smaller than some of the scales found on the external surface of the body. 

 Rose calls attention to the fact that in Chlamydoselachus the dentine (illustrated by his 

 Fig. 10) develops in fundamentally the same way as in mammals. 



Text-figure 11. 



Text-figure 12. 



The first two teeth (x 45) of the third 



row of the upper jaw of a 340-mm. 



embryo of Chlamydoselachus. These 



teeth are united at their bases. 



After Rose, 1895, Abb. 6. 



