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Show 322 DR. H. GADOW ON EVOLUTION [Mar. 20, with tiny scales, and as a rule these are sharply marked off against the much larger ventrals. Femoral pores.-The commonest numbers are 20 and 21, the usual range extending from 19 to 23. Quite exceptional was the occurrence of 17/20 in a tall specimen from Ayutla, and another from the foot of Los Cajones. 18 did not occur. 23 pores, mostly on one side only, were observed 4 times. Length of hind limb.-The claw of the fourth toe usually reaches the ear, but in one specimen from Ayutla it only reaches the arm, whilst in another from exactly the same locality the limb is so long that the claw extends to the eye. Coloration of under parts.-The collar" is normally black in both sexes. Even in the young of only 50 or 56 m m . in length, it begins to become dusky or speckled on the sides. Sometimes, however, even in adult males during the breeding-season, the collar is not black but leaden, in rare cases almost dull whitish. In other cases the black spreads sometimes onto the neighbouring parts of the throat; in a specimen from Los Cajones the whole throat is blue-black, and in all the four sr)ecimens from San Domingo, Isthmus, the throat is black. In the majority of cases the throat is whitish or pale lead-colour. Lastly, in the adult males, and even in some females of the specimens which I observed and caught at Agua fria, the throat was light brick-red, but this red fades away completely in spirit-specimens. Chest and belly are whitish or greenish yellow ; in the males more or less suffused with dark blue, chequered towards the sides and on the ventral surface of the thighs. But this blue, rarely verging towards black, is only suffused and is restricted to the deeper, cutaneous strata of the scales. The under surface of the tail is white, bordered or chequered with blue on the sides. The cobmr-pattem of the back (text-figs. 74, 75, and 81 E) consists of an almost black to dark olive-grey to ashy-brown ground, broken by 6 to 9 longitudinal rows of white, slightly greenish or yellowish colour. These rows are either entire stripes, or one or all of them may be broken up into coherent beads, or into separate spots. This breaking up of the stripes into spots proceeds upon a definite plan. First, the breaking-up increases with the size or age of the lizard, but this does not exclude the existence of old and large specimens which retain their stripes throughout life. Secondly, the breaking-up, or the frequency of beads or spots, proceeds from the central stripe or pair of stripes towards the flanks. In this way then in the 7- or 9-striped specimens the central stripe, number 4 or 5 respectively, is the first to break up. In fact, there are none with 9 complete stripes, and there are but few with 7 complete stripes. Specimens with 8 complete stripes (the stripes 4-4 running parallel, or being joined into an unpaired one on the neck) are not uncommon, but more frequently they are dissolved into many white and bright spots. Then follows pair 3-3, then pair 2-2, which is often represented by a series of |