426 OLIVER p. HAY 



one can see why they might coossify with the neurals; other- 

 wise, not. 



The marginal rows of osseous elements in the armor of the 

 leatherback are regarded by Versluys as being equivalent to the 

 peripheral bones of the thecophores and both as belonging to 

 the epithecal skeleton. In Archelon a supramarginal bone has 

 been found to articulate with two of the peripherals. The supra- 

 marginal is an epithecal bone; therefore, argues Versluys, the 

 peripherals are likewise epithecal bones. However, one might 

 insist with equal right that these peripherals are thecal elements 

 because in the great majority of turtles they articulate with the 

 costal plates and with the nuchal. Horny scutes alternate in 

 the same way with both the costal plates and the peripherals. 

 Versluys recognizes that in the case of the other scutes they cor- 

 respond with epithecal bones that have disappeared; but he 

 appears to believe that the scutes overlying the peripherals 

 form an exception. It would be very remarkable if the scutes 

 once coincided with the epithecal elements and later came to 

 alternate with them as they do with the thecal bones. We 

 ought at least to have satisfactory evidence that such a change 

 has been effected. 



Inasmuch as the plastral bones, omitting the epiplastrals 

 and the entoplastron, are derived from gastraUa, the peripherals 

 of each side may possibly have originated from an outer longi- 

 tudinal row of gastralia. 



Those investigators who have access to skeletons of the South 

 American pleurodire Chelys are invited to make a study of its 

 shell. In the United States National Museum there is a mounted 

 skeleton which presents some features which appear to have a 

 bearing on the relationships of the various groups of the Testudi- 

 nata. This skeleton has the catalogue number 29545 and the 

 record shows that the animal came from Caicara, Venezuela. 

 As is well known, there is, on the lateral keels of the species of 

 this genus, near the hinder border of each costal scute, an ele- 

 vation, or boss. In the skeleton mentioned there is found on 

 each of the bosses of the second scute areas, right and left, a cap 

 of thin bone which is joined suturally to the underlying costal 



