rLEruoniK.v. 187 



Supcrfam. 15. rLEURODIRA. 



Emydea monlmopelvca, Stannius, Zoot. Ampk. 1854. 

 ricurock'ivs, arm/, Sitj>pL Cat. Sh. Ilrpl. i. 1870. 

 rieiti-odira, C"pe', Proc. Atner. Assoc. Ailr. >Sr. xix. 1870, p. 2;]5. 

 Peltochelyida}, part., Seeley, Q. Joiirn. Gcnl. Soo. xxxvi. 1880, p. 112. 

 Paradiacostoidea, part., Baur, Zuol. Ajiz. 1887, p. 00. 



Neck beiulin::: laterally ; cervical vertebnu with strnno; transverse 

 processes, the cup-aiul-ball articulaliou single throughout : ccnlruiu 

 of the last cervical articulating with the centrum of the first dorsal. 

 Mandible with an articulary condyle fitting into a concavity of the 

 quadrate ; outer border of tympanic cavity comi)letly encircled by the 

 quadrate ; pterygoids very broad throughout, forming wing-like 

 lateral expansions, and in contact on the median line. I'elvis 

 auchylosed to the carapace and plastron. Digits with not more 

 than three phalanges. Epiplastra in contact with hyoplastra ; 

 entoplastron oval or rhomboidal. A complete series of marginal 

 bones connected with the ribs. 



PoKSAL Vertebral Columx axt> Carapace. — The number of 

 vertebra) between the last cervical and the first caudal is ten or 

 eleven in all recent Pleurodira, instead of twelve as in all Cryptodira ; 

 the reduction being due to the absence of true sacrals or to the 

 presence of but a single one, althongh the last or the last two dorsals 

 may assume, in the adult, the character of sacrals. The first dorsal 

 centrum is proportionately more elongate than in the Cryptodira, and 

 may C(iual the second in length. The centra are more or less com- 

 pressed, except in Chdys, where they much expand towards each 

 end for union with the proximally dilated extremities of the ribs. 

 In the latter genus, the attachment of all the ribs except the first 

 and last two is intervertebral ; in the other genera, this is the case 

 only with the second to fourth or fifth inclusively. 



The nuchal is usually as long as broad, or longer than broad. 

 The neural series rarely (SternofJufrus derhianvs) contains more 

 than seven plates {Chehjs, J/i/drasjns, Iltjdromcdusa, Pelomcdusidie 

 generally) ; there is a pretty complete gradation between such a 

 series and their total absence (Chelodina, Platemys, Emydura, 

 Eheya) : if present, these plates are hexagonal, and short-sided in 

 front. Costal plates normally number eight pairs ; but in a speci- 

 men of Pelomedusa I find nine pairs, and in another nine plates on 

 one side and the normal number on the other. The carapace is 

 fully ossified in all adult Pleurodira, and the marginals number 

 twenty-three, except in Carettoclielys, which has only twenty-one. 

 A single pygal is present, and in none of the recent forms does it 

 come in contact with the neurals. 



Plastkox. — The nine usual bones compose the plastron in the 

 Chelydid.T ; in the Pelomedusidte the number is increased to eleven, 

 the additional elements being the mesoplastra, situated between the 

 hyo- and hypoplastra. The plastron joins the carapace by suture, 

 and the axillary and inguinal buttresses are usually strongly 



