76 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



their outlines more oval than triangular, the third and fourth toes and 

 second and third fingers more nearly equal. The development of the 

 different embryonic conditions may be carried on very unequally in 

 different specimens, so that one cannot see the true specific charac- 

 ters in small individuals, or even in large ones in which there is the 

 slightest indication of the branchial slits or theit" tufts. 



The same adult individual differs, too, in different seasons. While 

 some species appear to reside almost entirely in water, others do so only 

 partially. Even the same species may pass a more aquatic life in one year 

 than in another. A. more persistent residence in water is shown by the 

 broader and more depressed digits, higher and more compressed tail, and 

 more or less decided ridge (sometimes even membranous). I have no 

 doubt that an animal while possessing these features in marked degree 

 when in the water would lose them to a measurable extent after a 

 lengthened residence on land. This aquatic habit is generally greatest 

 during the breeding season. 



The preceding paragraph is taken from Professor Baird's manuscript. 

 I will further extend and illustrate the same, and add that the names A. 

 californiense and A. maculatum have been applied by Gray and Hallowell 

 to forms of this species. 



Various changes of form during the late metamorphosis of this ani- 

 mal have been already enumerated in the prefatory remarks on the 

 genus. A feature of differeuce mentioned above— the varying length 

 of the fourth digit — appears to be quite independent of other develop- 

 mental conditions. In a specimen in the Museum of the Philadelphia 

 Academy from Kansas, this digit has but three phalanges on both feet; 

 in another locality three on one, four on the other foot, and the same 

 occurs in JSTo. 3994, of the National Museum. In all the other specimens 

 at my disposal they are, as in this section of the genus, 4-4. 



The varieties of this species which may be distinguished by their 

 coloration are as follows : 



a (Californiense.) Blackish, with slightly paler belly; a series of 

 large, oval, yellow spots on lower part of side and tail (in one specimen 

 a few on each side of dorsal line). System of mucous pores well devel- 

 oped, especially below ramus of the jaw on each side. From California 

 only; eight specimens ; Ko. 4081. 



/? Brown, yellowish below; larger lateral and smaller dorsal yellow 

 spots, irregularly arranged. Fewer mucous pores on each side the 

 gular region. Fourteen specimens ; mostly from Kansas and Nebraska, 

 one from Missouri, one from latitude 38°, two from New Mexico, and 

 two from Chihuahua; Nos. 4065, 4040, 3955a, 4062, 4084, 4908, 3984a. 

 The type of A. nebulosum belongs here. There is no material difference 

 between this and the coloration of A. tigrinum. 



y Ground brown, crossed by transverse yellow bands, which inoscu- 

 late more or less on the dorsal region, so as to obscure, sometimes almost 



