0. P. Hay — Fossil Turtles in the Marsh Collection. 269 



eximius, which has nine pairs of costal plates. Dr. George 

 Baur referred to a specimen of Malacoclemmys geographica, 

 having nine costals. Dr. Bonlenger, in his Catalogue, p. 187, 

 states that in a specimen of Pelomedusa he found nine pairs of 

 costal plates ; in another, nine plates on one side and eight mi 

 the other. Is it possible, therefore, to determine which costal 

 and peripheral bones, and which vertebral, costal, and marginal 

 scutes, in the specimen at hand, are the intercalated ones % 



Figure 4. — Chrysemys wyomingensis. 

 vidua! as that of figure 3. 



Diagram of plastron of same indi- 



It seems to the writer that there can be no question that the 

 six anterior neural bones and the six anterior pairs of costals, 

 together with the peripherals in contact with the latter, corre- 

 spond exactly with the six anterior neurals, the six anterior 

 pairs of costals, and the contiguous peripherals, of the type 

 specimen of Chrysemys ivyomingensis, or, indeed, of any other 

 member of the Emydidse. It appears to be quite as certain 

 that the seventh pair of costals corresponds with the seventh 

 pair in other emyds. Each is crossed at its upper end by a 

 portion of the longitudinal sulcus, and is in contact with a 

 neural, probably the seventh, and with that behind it. 



If, now, one begins at the posterior margin of the shell and 

 works forward, certain conditions may be established. As 

 usual, a pygal peripheral is present. In front of this comes a 



