468 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.59. 



upon each scale of the shield, and none upon the marginal scales; 

 as it advances in age new dots appear, one by one, upon each scale, 

 until they become very irregular, and extend to the margin of the 

 shield. I have, however, seen old specimens that were entirely 

 black, and others in which the dots remained few and regular." 



There are in the National Museum seven very young specimens of 

 this species, with a carapace varying from 28 to 33 mm. in length. 10 

 In only one individual are the marginals free from spots. The 

 others have single spots on from 8 to 18 marginal scutes. The 

 specimen (No. 23331, U.S.N.M.) with spots on 18 scutes is the 

 youngest of all, the umbilical aperture not yet being closed by shell. 

 It measures 28 mm. in length. The other specimen (No. 12701) of 

 this length entirely lacks spots on the marginals. Despite Agassiz's 

 statement that the newly hatched young are without spots on the 

 marginals, the specimen which he figures u has spots on two marginal 

 scutes on one side. Dr. H. L. Babcock, to whom I have recently 

 written for information on this subject, informs me that of the two 

 newly born young available to him for examination one has three 

 spotted marginals on each side and the other four. From this it is 

 evident that the statements of Agassiz and Yerkes with regard to 

 the absence of spots on the marginal scutes in the newly hatched 

 young are not true of all specimens. It is interesting to note that 

 the color characters distinctive of the sexes can be clearly seen in 

 these very young specimens, although the structural characters of 

 tail and plastron are not discernible. 



Babcock has recorded the fact that the males are less in evidence 

 in late summer and fall than the females, which accords with my 

 own observations. Most of my males were taken in March and 

 none later than May. My earliest date of observation of the species 

 is March 5, 1910, when a female was collected in North Easton, 

 Massachusetts; my latest December 6, 1912, when I saw two, one 

 of which, a female, was collected, in a pool in woods in Stoughton. 

 I have the following notes on the development of eggs : A female col- 

 lected on April 11, 1908, contained nine well-developed eggs in the 

 yolk. One taken on June 19, 1908, contained three mature eggs, 

 which are still in my collection, and eight in the yolk. One taken 

 on March 29, 1909, held nine round eggs in the yolk. The specimen 

 captured on March 5, 1910, contained three eggs in the yolk, about 

 14 mm. in diameter, and some smaller ones. The one taken on 

 December 6, 1912, contained two eggs in the yolk, about 1 cm. in 

 diameter, as well as smaller ones. 



"> Babcock (Mem. Boston Soc. Nat. Hist., vol. 8, p. 39S, 1919) gives the length of the carapace in the 

 newly hatched young as 26 mm., at the end of the first month 30 mm., and at the end of the second month 

 32 mm. 



»i Contr. Nat. Hist. U. S., vol. 2, pi. 1, fig. 7, 1857. 



