310 SCIENCE PROGRESS 



As regards the existence of three closely allied species on 

 Albemarle, the largest island in the Galapagos group, it is 

 important to mention that one of these, T. vicina^ is found in 

 the neighbourhood of Iguana Cove, on the south side of the 

 island, whereas T. microphyes inhabits Tagus Cove, which lies 

 to the north, separated from the first-named locality by a 

 volcanic range absolutely unsurmountable by these reptiles. 

 The precise portion of the island inhabited by the third species, 

 T. iiigray does not appear to have been ascertained. 



When Darwin visited Chatham Island, during the cruise 

 of H.M.S. Beagle^ he found tortoises abundant, and has given 

 an admirable account of their habits. 



Leaving the modern island species, both living and extinct, 

 attention may now be directed to their continental relatives of 

 earlier periods of the earth's histor}^ The first of these made 

 known to science was the gigantic Siwalik tortoise, Tcstudo, 

 or Colossochelys^ atlas, from the Lower Pliocene strata of the 

 Siwalik Hills of India, described by Falconer in 1844. On a 

 previous occasion I have expressed the opinion that the nearest 

 living relative of this species is the Malay brown tortoise 

 {T. emys) but I now believe this position to be occupied by the 

 African spurred tortoise (7". calcarata), which is one of the largest 

 existing continental species, and agrees with its gigantic extinct 

 relative in the absence of a nuchal shield and also in the horn- 

 like form of the front termination of the plastron. The Siwalik 

 tortoise is by far the largest known member of the whole group, 

 the length of the shell as restored by Falconer being no less 

 than eight feet, although it is possible that there may be some 

 exaggeration in the size of the restoration. 



In those dark pre-Darwinian days, when the geographical 

 distribution of animals was scarcely studied, the importance 

 attaching to the discovery of the Siwalik tortoise was very 

 imperfectly realised or, in fact, not realised at all. The discovery 

 served, however to prove, firstly, that giant tortoises are not 

 confined to islands ; secondly, that during the later Tertiary 

 periods they existed side by side with some of the largest land 

 mammals the world has ever produced. 



Later on remains of two giant tortoises {T. Icbcronis and T, 

 perpiniana) were discovered in the Lower Pliocene deposits of the 

 south of France ; whilst those of other species have been obtained 

 from the rock-fissures of Malta, from the Miocene of Nebraska 



