260 AMERICAN TESTUDINATA. Part IL 



Thus we have two diiferent modes of growth in the dermal plates of Testu- 

 dinata: that of Eretmochelys on one hand, and that of Testudo on the other. 

 Between these extremes, we have every possible intermediate feature. Thus, we 

 find that in the Chelonioidas and Emydoidge, though the plates are not free 

 behind as in Eretmochelys, but on the contrary lie Avith their whole under sur- 

 face upon the stratum Malpighii, as in Testudo, they still grow almost exclusively 

 in front and on the sides, showing only small additional stripes behind, or none 

 at all. This is still more strikingly exhibited in the Cinosternoidae, and here it is 

 in the direction of the Eretmochelys, as they show an evident inclination to an 

 imbricated position of their plates. It is already visible in Cinostei-non, especially 

 in Cinosternon flavescens, but still more in the Ozotheca triquetra of our South- 

 ern States, and also in our Northern Ozotheca odorata, when young. I have 

 ah'eady had occasion to allude above to the moulting of the epidermis when 

 speaking of Sphargis, Trionyx, and Eretmochelys ; but I am persuaded that such 

 a change in fact takes place in all Turtles. In Chrysemys picta, and in sev- 

 eral other fresh-water Turtles, such as Trachemys elegans and scabra, Ptychemys 

 concinna, Graptemys Lessueurii, etc., I saw in the spring the uppermost layer of 

 the dermal plates cast off at once as one continuous, thin, mica-like scale all over 

 the plate, and under it the fresh epidermis, showing beautifully by its transparency 

 the colors of the Malpighian layer. This reminded me very much of the moulting 

 of Snakes; but the difference consists in this, that in Snakes the epidermis is cast 

 off as one continuous skin from the snout to the end of the tail, while in Turtles 

 each scale casts its epidermis for itself In Testudo, the casting off of the old epi- 

 dermis is very different in different species, and even in different specimens of the 

 same species.^ I have seen in many adult specimens of Xerobates carolinus, and 

 still more distinctly in some old specimens of Testudo radiata, the central plate 

 of the scales, that is the plate of the first year, perfectly preserved with all its 

 fine granules, so sharp indeed that it seemed as if nothing had been cast from their 

 surface, while others were entirely worn out. These facts show that further obser- 

 vations are very much needed respecting the moulting of the Keptiles. Indeed, this 

 subject requires to be studied anew in all Vertebrata.^ 



other specimens of Gopher, which have the same ^ I mean here particularly also the moulling of 



mode of life, exhibit all the sculptures of their Mammalia and Birds, which is by no means so fully 



plates? We find the same difference between the understood as it would appear from our handbooks, 



specimens of Cistudo virginea, and still more between D. Weinland has presented interesting remarks upon 



those of Glyptemys insculpta, the smooth variety this subject in a paper read before the Boston So- 



of which has been described as a distinct species ciety of Natural History in the beginning of this 



under the name of E. speciosa. year. See the Proceedings of the Boston Society 



' See, above, p. 259, note on Gopher and Cistudo. of Nat. Hist, for 1856. 



