Chap. III. 



GENERA OF CHELYDROIDiE. 



417 



than in Gypocholys, and almost disappear late in life. The marginal rim pro- 

 jects only slightly at the sides beyond the carapace ; its front end is much less 

 arched backward than in Gypochelys. There are a pair of scales on the nose, above 

 the horny sheath of the jaw. There is no row of scales between the marginal 

 and costal rows. The scales on the plastron are less numerous than in G^po- 

 chelys ; one large one covers the whole bridge inside of the row of three which 

 curves its outer edge. There are only two papilln3 under the chin. 



Chelydra serpentina, Sckw} This is the well known Snapping Turtle of the 

 United States, one of the most widely distributed species of this continent. It 

 is found from Canada and Maine to Florida, and westward to the Missouri and 

 to Louisiana. I have seen specimens from Ohio, from Indiana, from Iowa, from 

 Missouri, and from Tennessee, not to speak of the Eastern and Middle States, 

 where it is everywhere common; but I still entertain some doubts as to the iden- 

 tity of the specimens from the Southern States.^ The color varies from light to 

 dark brown. Its growth is much more rapid during the first ten or twelve 

 years of its life than afterwards, as may easily be ascertained by a comparison 

 of the relative distance of the lines of growth in the centre and at the edge of 

 the scales of adult specimens.^ It is reported, upon reliable authority, that a 

 specimen, marked forty-five years ago, only increased one inch in that time. 



The fossil species referred to the genus Chelydra seem to belong to two dis- 

 tinct genera, resembling more closely in some respects the genera Chelydra and 

 G3'pochel3\«, while in other respects they are more clo.sely allied to Platysternum, 

 judging from the greater width of the anterior end of the sternum in Chelydra 

 Murchisoni, and of the posterior end in Ch. Dechenii.* 



* Although Linnceus mentions Algiers and China 

 as the home of his Testudo serpentina, there can be 

 no doubt tiiat it is our species, and that he was mis- 

 taken as to its origin, the genus Chelj-dni being ex- 

 clusively Nortli American. Pennant mentions it as 

 Testudo serrata, and Shaw as Testudo longicauda. 

 The names under wiiicli it is most frc(iueiitly ipiotcd 

 are Chelydra serpentina, Chelonura serpentina, and 

 Eraysaurus serpentinus. 



^ Speciniens from Moliiie and New Orleans show 

 a wider emarginatiun between the middle pair of the 

 marginal plates of tlie hind margin than northern 

 ones, and the keels of the back are less prominent. 

 There are some other difterenecs in the scales upon 

 the bridge between the plastron and the shield; but I 

 have not seen a sutricient number of specimens to be 



o3 



positive that all those found at the south agree in this 

 respect, and constitute a distinct species. At all 

 events, however, it is a remarkable variety, which 

 does not occur at the nortli, and which I shall label 

 Chelydra emarginata in my collection, until I have 

 better opportunities of ascertaining the value of the 

 diHerences thus far noticed. 



' Judging from the lines of growth, specimens six 

 and a half inches long and five and a half inches 

 wide are only twelve years old ; while others, which 

 measure not more tiian twelve inches in length and 

 nine and a quarter in width, are at least thirty-eight 

 years old. 



* Chelydra Murcliisonii, Bell, (Trans. Geol. Soc. 

 Lond.. 2d ser., vol. 4, p. 279, pi. 24 ; H. von Meyer, 

 zur Fauna der Vorwelt, p. 12, pi. 11 and 12, and Pa- 



