420 SCIENCE PROGRESS 



of Organic Structure," by Osborn {ibid. August 191 7) ; and 

 " Studies on Inbreeding. VII. Some Further Considerations 

 Regarding the Measurement and Numerical Expression of 

 Degrees of Kinship," by R. Peare (ibid. September 191 7). 



PALEONTOLOGY. By VV. P. Pycraft, F.Z.S., A.L.S., F.R.A.I., British 

 Museum (Natural History), South Kensington, London. 



The interpretation of the strange, spiral clusters of teeth 

 belonging to certain primitive Palaeozoic sharks — Campodus, 

 Helicoprion and Edestus — is a task of no small difficulty, but 

 a material advance has been made this year in the decipher- 

 ment of these puzzling relics by Dr. A. Smith Woodward 

 (1), whom Fortune favoured by throwing in his way a 

 finely preserved fragment of a jaw — apparently the pterygo- 

 quadrate — with its attached teeth, belonging to a species of 

 Edestus which proves to be new to Science, and to which has 

 been assigned the name of Edestus newtoni. The value of this 

 find, however, lies not in the fact that it adds a new name to 

 the number of known species, nor to the fact that only once 

 previously have such teeth been found attached to their 

 supports ; but in the clue it has afforded as to the evolutionary 

 history of these singular forms of teeth. 



In more than one instance there have been found with 

 these teeth other small " orodont " teeth whose presence, in 

 such an association, has been regarded as accidental. Hence 

 the smaller teeth were ascribed to a totally different fish, to 

 wit, Campodus, or Agassizodus. Such teeth are present in the 

 fragment now under consideration, and Dr. Smith Woodward 

 expresses his conviction that they are not only part of the 

 same dental system, but that they furnish the guide to the 

 course of evolution which has given rise to the larger, spirally 

 coiled, symphyseal teeth. He shows, in short, that the teeth 

 of the Edestus type are to be regarded as derived from the 

 Campodus type, and in this transition four well-marked phases 

 are to be seen. The first stage begins with the enlargement 

 of the middle part of the crown, and the reduction of its sides : 

 the second shows a further increase in the size of the crown, 

 and an enlargement of the hinder portion of its root. In the 

 third stage the crown consists of no more than the laterally 

 compressed middle part of the tooth. In the final stage the 



