

ORTHOGENETIC VARIATION IN THE SHELLS OF CHELONIA 1 . 



By HANS GADOW, M.A., Ph.D., F.R.S., 



University Lecturer in the Advanced Morphology of Vertebrates and Strickland Curator 



in the University of Cambridge. 



With Plates XXIV— XXV. 



Dr Willey has handed over to me 20 new-born specimens of Thalassochelys caretta, 

 the Loggerhead, collected by him from one nest in New Britain or Neu-Pommem. 

 He preserved them after noticing that they exhibited great variations, in so far that 

 none of them had the normal number of scutes. 



I have supplemented this material by examination of the specimens in the British 

 Museum of Natural History, and I am indebted to Dr Van Lidth de Jeude and 

 to Dr Oudemans for photographs and descriptions of others in the Leiden Museum, 

 and in the collection of the Royal Zoological Society " Natura Artis Magistra " at 

 Amsterdam. I am now acquainted with no less than 76 specimens, ranging from the 

 new-born to the adult. 



Mr G. A. Boulenger, F.R.S., has also kindly helped me with valuable additional 

 material and advice. 



It is a well-known fact, at least to herpetologists, that this species of Turtle 

 frequently possesses one or more "supernumerary scutes" and a critical study of these 

 variations has led to what I take to be an explanation of their meaning. 



In the following list of the specimens examined " size " is expressed by the length 

 of the carapace in inches. The number of marginals is 13 on either side, unless 

 noted differently. 



B.M. means that the specimen is in the British Museum. 



For simplicity's sake all the median epidermal scutes are mentioned as neurals, 

 including the first or so-called nuchal. 



1 A condensed account of this investigation was read, supplemented by diagrams, at a Meeting of the 

 Cambridge Philosophical Society on Monday, November 14th, 1898. 



w. in. 30 



