42 Dr. G. Baur on Meiolania. 



formed by the connexion of the neuroids with the first inter- 

 centrum (atlas-ring of birds and mammals). Such a ring 

 does not exist in the Pleurodira, so far as I know. If the 

 atlas of a Pleurodiran is macerated the intercentrum, if not 

 coossified with the centrum, becomes free ; it does not remain 

 in connexion with the neuroids ; these generally are united 

 with the centrum or may become free, as in the Podocnerai- 

 did^ {Podocnemis Dumerlliana and expansa) and some Chely- 

 didffi [Elseya according to Vaillant) . But if we macerate the 

 atlas of a Cryptodiran we never find, so far as I know, that 

 the neuroids of the atlas remain in connexion with the cen- 

 trum ; the neuroids of the atlas are connected with the 

 intercentrum, or all parts may become separated, as in the 

 Chelydrida3, Cheloniida3. This I wanted to state, and there- 

 fore I used the words " it is the centrum which supports the 

 neuroids of the atlas " in the Pleurodira. I excluded the 

 Podocnemididse, stating that the intercentrum also takes some 

 part. 



If we compare Mr. Boulenger's figures with these remarks 

 there seems to be considerable contradiction. 



In the specimen of Erymnocheli/s madagascariensis before 

 me the atlas is missing ; but for comparison I give an exact 

 figure of the first two cervicals of Podocnemis Dumeriliana. 

 Podocnemis and Erymnochelys are allied forms, and Erymno- 

 chelys is even not ditferent from Podocnemis according to Mr. 

 Boulenger. We may expect therefore that the first two 

 cervicals show in both similar conditions. As anybody will 

 see, my figures of Pod. Dumeriliana are entirely ditferent 

 from those of Erymnochelys given by Mr. Boulenger. The 

 neuroids are supported by the atlas centre, the intercentrum 

 is connected a little with the neuroids. The intercentrum is 

 very small compared with the centrum and projects below it. 



In Chelymys victorice we find a similar condition to that in 

 Pod, Dumeriliana ; but the intercentrum simply touches the 

 neuroids. The neuroids are more connected with the centrum 

 than in Pod. Dumeriliana. This condition is very much more 

 expressed in the following genera of the Chelydidaj — Chelys, 

 Hydromedusa^ Chelodinaj Hydrastis — and in the Sternothge- 

 ridaj ; in all these the neuroids have entirely gone on to the 

 centrum, with which they become ossified. 



In the Cryptodira the conditions are entirely different. 

 The most generalized arrangement we find in the Cheloniidte 

 and Chelydridte, in which the atlas-elements are only loosely 

 connected ; but even in these forms the centrum does not 

 support the neuroids. The coyincxion hetiveen these elements 

 is on a vertical ijlune, there is no sap^^ort ; the neuroids are 



