FUKTHER CONSIDERATION OF THE SHELL OF CHELYS 

 AND OF THE CONSTITUTION OF THE ARMOR OF 

 TURTLES IN GENERAL 



By Oliver P. Hay 



Associate of the Carnegie Institution of Washington 



1. SUPEKFICIAL, OR EPITHECAL, BONES 



In 1922 the writer contributed an article to the Journal of Mor- 

 phology ^ entitled " On the Phylogeny of the Testudinata and the rela- 

 tionships of DerTfiochelys." In this paper he called attention to the 

 occurrence of certain plates of bone on the carapace and plastron of 

 specimens of the South American pleurodire tortoise Ghelys, known 

 as the matamata. Some of the specimens studied belong to the 

 American Museum of Natural History, New York; others are pre- 

 served in the United States National Museum. In the case of some 

 of the shells there are many small bones irregularly distributed over 

 the upper and the lower surfaces. The origin and nature of these 

 were not determined. Other and usually larger bones occurred at 

 definite points and were interpreted as relics of a primitive super- 

 ficial armor retained nearly complete by the great sea turtle known 

 as the leatherback, or Dermochelys. These bones were shown to 

 occupy positions which correspond to 5 of the 12 keels which exist 

 on the shell of Dermochelys, 7 on the carapace, 5 on the plastron. 



After the publication of that article another matamata reached the 

 United States National Museum from the Zoological Park at Wash- 

 ington and, inasmuch as this specimen presents many such bones, it 

 is here described and illustrated by reproduced photographs. (Pis. 

 1 and 2.) From the front of the carapace to its rear the length is 

 13.5 inches (338 mm.). As in other specimens, there are on the cara- 

 pace three prominent keels, a median and two lateral. The median 

 keel presents five bosses or tuberosities, one at the rear of each verte- 

 bral scute. The hinder two are high and pointed. In each lateral 

 keel are four such tuberosities, one at the upper rear corner of each 

 costal scute. The marginal bones (peripherals) have each a projec- 



> Vol. 26, pp. 421-445, wi+h 2 pis. 



No. 2724.— Proceedings U. S. National Museum, Vol. 73, Art. 3. 



76978—28 1 



