Dr. A. Giinther on Hjdromedusa. 423 



2. Hydromedusa depressa (Gray). 



ITi/dro medusa depressa, Gray, Cat. Shield iriept. p. 60, tab. xxvi. 

 Hydrotnedusa subdepressa, Gray, Proc. Zool. Soc. 1852, p. 134. 



Shell very flat ; dorsal scutes without any tubercles. 

 Nuchal large and slightly in contact with the first costal. 



Brazil. The specimen which is the type of //. depressa as 

 well as of H. subdepressa is still the only individual known of 

 this species. 



3. Hydromedusa Wayleri, sp. n. 



Hydromedusa Maxitniliani (nee Mikan), Wagl. Syst. Amphib. p. 135, 



tab. iii. figs. 25-42 ; Gray, Cat. Shield Rept. p. 59. 

 Chelodina Maxuniliani, Diim. & Bibr. p. 449 (part.). 



Tuberosities are persistent throughout life on the last two 

 vertebral and costal scutes. Nuchal very large and broad 

 and in contact with the first costal, the first vertebral having 

 an oblong form (but being only three fourths as wide as long) . 



An adult male with a shell 7 inches long, in the Natural- 

 History Museum, from Buenos Ayres, agrees well with 

 Wagler's figure and with the description of one of the two 

 specimens given by Dumeril and Bibron, who also assign 

 Buenos Ayres as the native country of this species. 



It is very probable that Hydromedusa tectifera, Cope (Proc. 

 Am. Phil. Soc. 1869, p. 147), from the Parana or Uruguay, 

 is identical with this or the following species, in which case 

 the name given by Cope would have priority. Although 

 Cope describes the forms of the nuchal and first vertebral 

 (the latter being nearly twice as long as wide), he omits to say 

 whether or not the nuchal is in contact with the first costal. 



4. Hydromedusa platanensis (Gray). 

 PI. XIV. 



Chelodina Maximiliani (nee Mikan), Dum. & Bibr. p. 449 (part.). 

 Hydromedusa j)latane7ists, Gray, Ann. & Mag. Nat. Hist. 1873, xi. 

 p. 302. 



Nuchal scute transversely broad (in the adult about thrice as 

 wide as long), but separated from the first costal by the produced 

 anterior corners of the first vertebral. Vertebral and costal 

 scutes with tuberosities which disappear with age, with the 

 exception of those of the last two vertebrals and costals. 



This is a large species, which was first noticed in this 

 Journal (/.c), the shell of a fully adult specimen being 9^ inches 

 long. It inhabits the Rio de la Plata and fresh waters further 

 to the south. The young differs so remarkably from the adult 

 that I append a detailed description ; it is figured on PI. XIV. 



This singular turtle reminds us at the first glance of the 



32* 



