125 



are in the National Museum, and I have also examined a number of speci- 

 mens of both the species in my own collection. I find that the size of the 

 head is not a specific, but a sexual, character, and that it is the 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, Malademys 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 I am quite certain that no ap- 

 preciable difiierences will be found between them, when we compare speci- 

 mens of the same size and sex. 



Another interesting matter pertaining to most, if not all, the spe< ies 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 observa- 

 tion that the male of the salt-water terrapin is small. Of the seven speci- 

 mens of M. geographica taken by myself at Lake Maxinkuckee, three had 

 the carapace 3f inches long, while the other four had a length of carapace 

 ranging from 6!^ to 9 inches. Dissections proved that all the small speci- 

 mens 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. oculifera 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 

 Cltehjdra serpentina that I have ever seen was a male, and I believe that the 

 males of the various speci<-s of the genus Chrysemys, as defined by Boulen- 

 ger, exceed the females in size. 



It is quite characteristic of the species of the genus Malademys to have a 

 prominent keel along the middle of the carapace, and this is often nodose. 

 In M. pseudogeographica the keel is nodose al) through life. However, all the 

 species, so far as we know, have these elevations 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 me- 

 dium-sized peas, four or five in number, lying along the back. The species 

 M. geographica, having such a nodose keel w^hile 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 

 life. The young of M. oculifera will undoubttdly be found to have a dis- 

 tinct and nodose keel. 



