160 KECORDS OF THE AUSTRALIAN MUSEUM. 



Atlantic Cit}-^, New Jersey, on the At laiitie Coast of tlie United 

 States, wliile ('helouia depressa is known from the East Indies, 

 Northern and North Eastern Coasts of Australia and Torres 

 Strait. 



The limited habitats of ('olpochel ijti and ('. ihji resign suufufest 

 that (1) these two species are moi'e recent specialisations,- and 

 (2) that they are weaker swimmers, lacking the nomadic 

 instincts of the better known forms. The distribution of each 

 points to their having arisen in the two great coral-reef areas 

 of the world, the former from a Caretta-Yx^e ancestor in the 

 West Indies, and the latter from a ('. //^//r^(^•-like stock in the 

 tropics of the Eastern Hemisphere. 



Dr. R. E. Coker-^ points out that, as Colpocheli/n breeds 

 considerably before Curetta, in fact in the winter instead of the 

 summei' months, this diffei'ence in bi'ceding habit may suggest 

 the possible means of isolation of the two forms in jiast times. 

 This cannot be said of ('. depres.ta however, for it bi-eeds all 

 the year round, but peculiarly with a slight falling off in the 

 months August to November which chiefly form the breeding 

 season of C. viydas. Nevertheless, that ('. depressa is a 

 weakei" swimmer than (\ riiiid(i.<< is evident, for the flippeis 

 are much smaller and not so well supported by hard, horny 

 plates, while the retlexed margins and broader body can.not lie 

 so well suited to a speedy passage through the wiitcr. It is 

 quite possible then, that tlie former character, ai-isini;' thrmigli 

 some local influence, nuiy have been a factor in tlie past 

 separation of C di-prcfr^K from n I', m i/ilidi-Wke anct'stoi-. 



The Ureen, Hawksl)ill, and Loggei'head turtles liave by 

 some authors*,^, been recognised as each constituting two 

 species, one confined to the Atlantic Oceans ami the other to 

 the Pacific and Indian Oceans. No clear definitions of the 

 Pacific species have yet appeareil. the Atlantic forms being 



- Tho presence of liit^lily developed ai-eol.e (see post), wliich I 

 regard as a specialised advance on the " larval shields" of C. niiitlns, aiitl 

 a slif^lit reduction in the exteut of the teiii])onil roof (see post), lend 

 supitort to this view. 



:' Ooker— Bull. N. Carol, (^eol. Surv., 14. 19()fi, p. (iO. 



•• Uarinan— Bull. Mus. Conip. Zool.. v., 1880, p. li>:{. and Hull. U.S. 

 Nat. Mus., 25, 1884, p. 301. 



6 Stejneger— Bull. U.S. Nat. Mus., 58, IWJ, p. 5(H). 



