The Jiatural History of the Frilled Shar\ 



311 



These statements have all been checked against the figures of the teeth referred to, 

 and we beHeve that, so far as we can judge from the structure of the teeth, Chlamydo' 

 selachus has no generic relationship with Diplodus { = Didymodus). With regard to its 

 affinities to Cladodus, Dr. W. K. Gregory comments as follows: ''Some authors regard 

 Chlamydoselachus as a living representative of the cladodont sharks of the Devonian and 

 Carboniferous periods, but later investigations indicate that it is only a deep'water 

 specialisation of a Meso2;oic group." 



The teeth of Chlamydoselachus (Text'figure 10) are barb'like, prehensile, and aUke 

 in both jaws. Those of Heptanchus (Text-figure 29) are adapted for cutting as well as 

 holding, and are not alike in upper and lower jaws. The decided differences between the 

 teeth of Chlaynydoselachus and Heptanchus — forms which are in many important respects 

 closely related — serve to weaken our faith in the validity of phylogenetic deductions 

 based on a comparison of present-day fishes with fossil forms that are known only by their 

 teeth. Generally speaking, in living fishes family differences in the teeth are great, gen- 

 eric differences are considerable, while specific differences are slight. But it should also 

 be borne in mind that the form of teeth is mainly an adaptive character, very subject to 

 parallelisms. 



FOSSIL CHLAMYDOSELACHIDS 



Interestingly enough, while the controversy above epitomised was raging, all the 

 contestants were unaware that as early as 1876 the fossil teeth of a true Chlamydoselachus 

 had been described. In fact this was not 

 known until Davis called attention to it in 

 1887, when the controversy had died 

 down. Furthermore, since our work on 

 this article began, the fossil tooth of an- 

 other species of this genus has been found. 

 Both of these finds will now be described. 



CHLAMYDOSELACHUS LAWLETI 

 FROM NORTHERN ITALY 



Great numbers of fossil sharks' teeth 

 have been found in northern Italy, and in 

 1876 Roberto Lawley described many of 

 these. Among them were certain remark- 

 able ones from the Pliocene beds of Orci- 

 ano in Tuscany. These he figured and 

 described without assigning any name to 

 them. In our Text-figure 30 we repro- 

 duce his drawings in the exact sise in 

 which he published them — i.e., lb is in 

 natural size, the others are approximately 



Text-figure 29 



Dentition of Heptanchus (J^otidanus) indicus Guv. 



a, teeth in function; b, teeth in reserve; u and I, upper and lower 



single teeth (XI). 



From Goodrich after Giinther. 



