1893.1 ^-'--L IBaur. 



ler belong to two different species. This is at once seen from the structure 

 of the squamosal and frontal. 



In the specimen of Peters the posterior ends of the frontals are very 

 slender and not connected with the very slender inner branches of the 

 squamosals. In the specimen of Wagler the posterior ends of the frontals 

 are well developed and united with the inner branches of the squamosals. 

 There is a frontosquamosal arch in Wagler's specimen, but there is only a 

 supraoccipito-squamosal arch in the specimen of Peters. 



Unfortunately, the skull of the type of Hydromedusa tectifera Cope is 

 not preserved, and it is therefore impossible to determine whether one of 

 the specimens figured by Peters and Wagler belongs to this species. In 

 spite of the papers of Dr. Giinther and Boulenger on the subject, it is 

 now again as undecided as ever. Further studies have to decide about it. 



The characters of the genus Hydromedusa Wagler. The skull of Hy- 

 dromedusa shows a peculiarity which separates it widely from its allied 

 forms, Chelys and Chelodina. In Hydromedusa the posterior nasal open- 

 ings are of enormous size and the pterygoids form their posterior and inner 

 border. In other words, the palatines have no inner process at all to con- 

 nect the vomer (Peters). This seems important enough to place Hydro- 

 medusa in a separate family, Eydromedusidm, with the following charac- 

 ters : 



Hy dromed usidw. 



A slender parieto squamosal-, or supraoccipito-squamosal arch. Posterior 

 nasal openings bounded by maxillary, palate, pterygoid and vomer; frontals 

 double; nasals free ; premaxillary double. 



I also propose to establish separate families for both C/ielys and Chelo- 

 dina, with thefollowing characters : 



ChelyidcB. 



A strong parieto -squamosal arch. Posterior nasal openings bounded by 

 maxillary, palate and vomer ; frontals double, no free nasals ; premaxillary 

 single. 



ChelodinidcB. 



No parieto -squamosal arch nor supraoccipito-squamosal arch. Posterior 

 nasal openings bounded by maxillary, palate and vomer ; frontal single,* 

 nasals free ; premaxillary double. 



The other genera of the Chelyidoe, in the sense of Boulenger, are : 



Rhinemysf Wagler, 1830 = Phrynops Wagler, 1830=Hydraspis (Blgr.) 

 -j- Rhinemys (Blgr.). 

 Platemys Wagler, 1830. 



• Baur, G., " The Pelvis of the Testudinata," Jnurn. Morph., Vol. iv, 1891, p. 352. 

 fBaur, G., "Note on the Genera Hydraspis and Rhinemys," Am. Nat., May, 1890, 

 p. 485, 



