230 L. C. Johnson — Structure of Florida. 



" wonder if the other legs of the double shell are not growing 

 inside." 



There seems to be absolutely no cooperation between the 

 left side and the right, and yet they repeatedly start at the 

 same time to do precisely the same thing, eat, swim, or walk. 

 When by any mischance it falls over on its back, the two heads 

 work in opposite directions to right the shell, and so without 

 help it could never, like an ordinary tortoise, extricate itself 

 from the predicament. 



The length and flexibility of each neck shows it has the full 

 number of cervical vertebrae, confluent at the first thoracic 

 vertebra. In other respects its skeleton is quite normal. The 

 dermal plates show a few unimportant variations. There is 

 the usual nuchal plate in front on the middle line, and two 

 pygal plates behind. Between these two points on either side 

 are twelve marginal plates : the usual though not invariable 

 number being eleven. On the right side an extra scute is 

 wedged in among the costal plates, making five on that side 

 to four on the other. The five vertebral or neural plates pre- 

 serve their relative positions, but have somewhat distorted 

 forms. The first of these is divided by a suture through its 

 length. The fifth is composed of four small irregular plates, 

 and presents a fissure where it did not unite on the middle 

 line. The plates of the plastron show but one irregularity, a 

 doubling of the gular plate. A suture is seen in the right 

 femoral plate ; and the right infra-marginal plates are united, 

 the left separate; but these are not peculiarities however. 



When the time arrives for the promised dissection of this 

 curious little monstrosity, I shall hope to find anatomical pecu- 

 liarities of some consequence. 



Paleontological Laboratory, New Haven, Ct., Sept. 4th. 



Art. XXIII. — The Structure of Florida ;* by Lawrence C. 



Johnson. 



The stratigraphy of Florida is as yet so little understood 

 that any notes upon it may be acceptable. 



The facts in this contribution can best be made clear by a 

 section across the peninsula through St. Augustine and Gaines- 

 ville. By this it will appear that at least all the northern 

 and middle portion of peninsular Florida may be divided longi- 

 tudinally into four regions, plainly marked by surface indica- 

 tions : (1) the " Gulf Hammock " in the west, (2) a central 



* Read before the American Association for the Advancement of Science at 

 New York, August, 1887. 



