0\ TIIR STAPI'S (IF CIIKI.OXIA DKI'UKSSA VRY . 177 



base of a new one beneath wliich are developed othei- layers, 

 preserving the shape and size of the original areola. The 

 areolfe of these tortoises then, would appear to serve some 

 definite function throughout life and cannot in a true sense be 

 regarded as "larval" characters. In the case of the turtle 

 however, at the time of hatching, these shields have reached 

 their maximum develo])ment, and from then onwards, owing 

 to the wear and tear to which they are naturally subjected, 

 they become gradually reduced, till little more than a Hakey, 

 tissue-paper-like remnant remains. They are then slied, leav- 

 ing the bare scute of the adult. 



These " larval shields " occur in both Chelnnid uiijfhis and 

 ( '. depressa, but differ considerably in their degree of develop- 

 ment, and in no stage of the former can they be called ai'eolae. 

 The figures on Pis. xix. and xx. represent almost identical 

 stages of the two species and a comparison shows that in C 

 VI y das they ai'e much thinner and devoid of the deep pits shown 

 in the other species. The material in the Australian Museum 

 leads me to the conclusion that the larval shields are shed 

 much earlier in the common Green Turtle than in ('. depressa. 



The reduction due to erosion of the areolae in Chelonia 

 depressa is veiy noticeable when the specimens are placed in 

 order of age. This can be followed by examining in turn the 

 newly hatched example (PI. xix.), the somewhat older specimen 

 beside it, McCulloch's figure-^ of his type, and the semi-mature 

 specimen on Pis. xxi. and xxii. Figs. 39 to 41a and b sliow 

 this reduction of the areolae on the head shields of specimens 

 Nos. 1, 4, 6, and 7. The newly hatched examples possess 

 thick, deeply pitted larval shields which become gradually 

 reduced along the series of older specimens till, in the type 

 example they are reduced to the thickness of paper with 

 frayed, mica-like edges, and on which the gi'anulations remain 

 as the faintest impressions. At some stage between that of 

 the type example and specimen No. 7, the areolfe are shed, 

 leaving the smooth, almost leathery scute. 



Although the areolae of C. depressa differ fi'om those of 

 Testudinian Tortoises in the absence of any trace of post- 

 embryonic growth, they must be considered as morphologically 

 homologous, and, whatever may be their use in the land 

 tortoises, there seems little doubt that in C. depressa they 

 function in the young stages simply as a protection for the 

 underlying scutes, which are of an unusually soft nature. 



-5 McCulloch — Eec. Austr. Mus., vii., 1908, pis. xxvi. and xxvii. 



