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CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



OsTEOLOGiCAL DIFFERENCES. — Those wliicli have been con- 

 sidered of taxonomic value are mainly differences which 

 appear in the skulls, cervical vertebrae, shoulder-girdle, pelvis, 

 and large limb bones. As in the case of the shell, these are 

 differences of proportion. It has been stated that Tcstudo 

 becki and the Charles Island tortoise (T. dcphantopus s. gala- 

 pagocnsis) differ from the other races in having the third 

 instead of the fourth cervical vertebra biconvex. This con- 

 dition in the type of T. becki is an individual variation, since 

 it is the fourth vertebra which is biconvex in my series of 

 seven specimens from Bank's Bay. The condition doubtless 

 is anomalous also in the Charles Island specimen. The dif- 

 ferences in proportion of the bones of the limbs and neck cor- 

 respond with the relative length of these parts in the variods 

 races, the number of bones being the same in all. They are 

 proportionally shorter in the dome-shaped races, and longer 

 in those in which the carapace is elevated and compressed 

 anteriorly. These differences are shown in the measurements 

 of the limbs and neck given with the description of each race 

 or species. Certain differences in the skulls of the tortoises of 

 the various races have been pointed out by Dr. Giinther. I 

 believe that the differences he has indicated are all merely 

 individual variations. In a series of 24 skulls from Vilamil, 

 Albemarle, I find all of the variations which Dr. Giinther 

 mentions ; and upon careful comparison of this series with one 

 skull from Hood Island (No. 8125), one from Indefatigable 

 (No. 8381), one from James (No. 8105), three from Dun-' 

 can (Nos. 8378, 8379, and 8380), four from Chatham (Nos. 

 8127, 8128, 8130, and 8131), and one from Iguana Cove 

 (No. 8179), I can find no constant differences in the skulls 

 of the various races. In the skulls from Vilamil, the frontal 

 region may be flat or somewhat convex. The occipital spine 

 may be short or long, not reaching the posterior borders of 

 the mastoid processes or projecting far behind them, and 

 may or may not rise much above the level of the skull. There 

 is much variation in the shape of the tympanic case and cavity. 

 The fossa in front of the occipital condyle may be deep or 

 very shallow. The tuberosity for the temporal muscle may 

 be quite small or very largely developed. The nasal opening 

 may be as high as broad, or broader than high. The palatal 



