ae 
pte PROCEEDINGS OF THE NATIONAL MUSEUM. 383 
females which have the large heads. The heads of the males are much 
smaller and also more pointed. I believe that the same statements are 
true regarding the salt-water terrapin, Malaclemys terrapin, although I 
have not been able to examine a sufficient number of specimens to be 
certain about it. With regard to the other two species referred to [ 
am quite certain that no appreciable differences will be found between 
them, when we compare specimens of the same size and sex. 
Another interesting matter pertaining to most, if not all, the species 
of this genus is the size of the male as compared with that of the 
female. Le Conte is the only author who has, so far as I am aware, 
made the observation that the male of the salt-water terrapin is small. 
Of the seven specimens of M. geographica taken by myself at Lake 
Maxinkuckee, three had the carapace 33 inches long, while the other 
four had a length of carapace ranging from 62 to9 inches. Dissections 
proved that all the small specimens were males and the large ones 
females. The same statements are true of such specimens of M. 
pseudogeographica as I have examined. All the specimens of M. ocul- 
ifera BAUR in the National Museum are, judging from the form of the 
shell, females; and they are all large specimens. Both Agassiz and 
Baur have observed that the males of Trionyx spiniferus are smaller 
than the females. On the other hand, the largest specimen of Chelydra 
serpentina that I have ever. seen was a male, and I believe that the 
males of the various species of the genus Chrysemys, as defined by 
Boulenger, exceed the females in size. 
It is quite characteristic of the species of the genus Malaclemys to 
have a prominent keel along the middle of the carapace, and this is 
often nodose. In M. pseudogeographica the keel is nodose all through 
life. However, all the species, so far as we know, have these eleva- 
tions along the keel when young. In some of the young of the salt- 
water terrapin I found that the nodosities were especially large and 
globular. They resembled greatly a row of medium-sized peas, four or 
five in number, lying along the back. The species M. geographica, 
having such a nodose keel while young, but losing it as age advances, 
must be regarded as attaining a higher stage of development than 
pseudogeographica, which retains this embryonic character throughout 
lite. The young of M. oculifera will undoubtedly be found to have a 
distinct and nodose keel. 
Agassiz (loc. cit. p. 260) discusses the various ways in which the dif. 
ferent kinds of turtles get rid of the older layers of the epidermis. He 
mentions certain species of fresh-water turtles, among them M. pseudo- 
geographica, in which he observed in the spring the uppermost layer 
of the dermal plates to be cast off at once as one continuous, thin, 
mica-like scale all over the plate. In a number of very young speci- 
mens of M. geographica taken at Lake Maxinkuckee, the outer layer of 
the epidermis was lifted up from the underlying layers by a quantity 
of fluid. This was preparatory, no doubt, to the casting off of the 
_ epidermal layer. 
