INTRODUCTION. 219 
actually but proportionately and are all comparatively rare. It must not be sup- 
posed that these species are in any wise ancestral the one to the other; .but are 
simply examples chosen as typifying arrested stages pointing out the path by 
which such a form as anthracinus, for instance, may have been derived from one 
like cinereus at first sight apparently wholly unrelated. The apparent dis- 
similarity is bridged over by a series of hypothetical ancestral intergrades which 
happen tobe illustrated by various scattered species. In anthracinus (syn. asper), 
copei (syn. picturatus) and scaber there is a distinct sexual dichromatism, the males 
being monochrome, the females fantastically banded and decorated with ocellate | 
spots. However, a similar dichromatism exists in decoratus and torret among 
the species having granular scales. 
A condition similar to this has been independently arrived at in some 
species of Gonatodes, far from closely allied. This apparently is not true of the 
Jamaican richardsonii for I have traced eight specimens, all banded and of this 
number both sexes were probably represented. Structurally this species is 
closely related to the three others but is more primitive in colouration, probably, 
and in lacking the middorsal zone of granules. This curious character has not 
been mentioned previously. It is found that in several, indeed, in most of the 
species with very large scales, there is a narrow zone of fine granular scales 
running down the middorsal region. This probably has been at least three 
times independently acquired in that the zone is rather wide and not very 
sharply defined in vincenti (St. Vincent) and macrolepis (St. Lucia); while festus 
(Martinique) shows no sign of a zone. The species from the Upper Lesser 
Antilles, pictus (St. Kitts), sputator (St. Eustatius) and elegantulus (Antigua) 
have a very narrow zone, sharply defined although the body-scales are not so 
very large. In Porto Rico, Mona, and the Virgin Islands (macrolepis), the local 
species although large scaled, has no middorsal zone. On the other hand, in 
Cuba, Haiti, and Andros Island there are very large species with very large 
scales, viz. scaber, copei, and anthracinus respectively which have the middorsal 
granular zone well defined. Thus it may be observed that the character appears 
in three separated groups of species. No explanation has been offered suggesting 
why this character should be acquired. It seems reasonable, however, that it 
may have to do with the flexibility of the body. The large overlapping scales 
tend to form a sort of cumbrous armour and the expansion and contraction of the 
body connected with breathing may be facilitated by this zone of small, non- 
imbricating scales lying upon a flexible integument. Analogous, but more 
obviously necessary, are the lateral grooves of soft skin or fine scales seen in 
