8 THE EEPTLLES OF EGYPT. 
colour-variation is such that groups of individuals, if judged only by their colour, 
would unhesitatingly be referred to distinct species. A most striking instance of 
this is the snake Homorelaps lacteus, the colour-variations of which have lately been 
made known by Mr. Boulenger 1 . 
When Geoffroy St.-Hilaire returned, in 1827, to the study of the crocodiles of the 
Nile, not only did he still regard C. suchus as a good species, but he went further and 
described three other species from the same river, besides it and C. niloticus. 
The first of these species, C. marginatus, was represented by mummies and by recent 
specimens. He states that " Les ecailles cervicales, dorsales, pelviennes et sexuo-caudales, 
ne different ni par nombre ni par la forme de ces memes ecailles dans l'espece prece- 
dente " (C. niloticus) ; also that "Les couleurs de cette espece, qui separement sont 
les memes que celles des autres crocodiles, different dans leur distribution respective. 
C'est le meme fond vert, mais il est masque par une si grande quantite de traits noirs, 
delies et rapproches, que cette derniere teinte domine. Les pecheurs de Thebes, 
m'ont parle de ce crocodile noir ; c'est ainsi qu'ils l'appellent." 3 Notwithstanding its 
close similarity to C. niloticus he held that it was distinguished from it by its nuchals 
always being more than two and not exceeding six in number, and by another 
character, viz. : — " Le bord jugo-temporal ne forme plus une ligne toute d'une venue, 
parfaitement droite, et uniformement soutenue a la hauteur de la plaque frontale ; 
mais il est remarquable par un relief tres prononce superieurement, beaucoup plus en 
arriere que par devant. En vieillissant, ces saillies deviennent des bosselures con- 
siderables. Le nom de marginatus m'a paru rappeler utilement ce caractere." Added 
to this, he considered that the way in which the colours were distributed entitled it to 
specific rank. He also attached some importance to the presence of 21 scales in the 
posterior portion of the tail, i. e. behind the junction of the dorsolateral ridges, as he 
had only met with 16 scales in that part of the tail of C. niloticus, and 19 in C. suchus. 
The swellings on the side of the head, supposed to be characteristic of C. marginatus, 
are also present in skulls which cannot but be regarded as referable to C. niloticus. 
They seem to be largely brought about by age, as they are always most pronounced 
in adults. 
Cuvier, in 1812, described a crocodile from the Senegal as C. biscutatus, distinguished 
by the presence of only two large pyramidal scales on the middle of the nape and two 
small ones in front. Geoffroy was uncertain whether it might not be the same species 
as his C. marginatus ; but in describing the fourth species of crocodile from the Nile, 
which he called C. lacunosus, and which had also only two nuchal scales, he says, 
" I know of no other crocodile distinguished by this feature, unless it be the biscutatus 
of M. Cuvier." C. lacunosus and C. complanatus were founded on mummies — the 
former on a specimen 2 m. 49G millim. in total length, and the latter on a still larger 
1 Cat. Snakes B. M. iii. 1896, p. 409. » Descr. de l'Egypte (8vo ed.), Hist. Nat. vi. 1829, p. 565. 
