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Mr. G. A. Boulenger on the Distinctive 
XLIX. — On the Distinctive Cranial Characters of the I guanoid 
Lizards allied to Iguana. By G. A. Boulenger. 
Shortly after the publication of the second volume of the 
British Museum c Catalogue of Lizards ’ Prof. Cope proposed 
an arrangement of the genera of Iguanina, i. e . of the genera 
closely allied to Iguana , u without abdominal ribs or free 
dermal margins of the digits, with the nostrils on the line of 
the canthus rostralis and not below it, and which possess the 
compressed form and other characteristics indicating an arbo- 
real rather than a terrestrial habit of life ” *. This arrange- 
ment is certainly no advance on that which I had previously 
followed, the only important innovation being the union of 
the genera Metopoceros and Cyclura under the latter name. 
His reasons for doing so are given in the following words : — 
u If the presence of the second row of femoral pores is not 
constant in C. cornuta , then the genus Metopoceros cannot be 
distinguished from Cyclura. Mr. Boulenger relies on the 
rather greater number of denticles in the lateral teeth in C. 
cornuta , but my specimens show a tendency to the tridentate 
form of G . nubila . The character is, I think, even if constant, 
insufficient for generic distinction.” Although agreeing now 
with Prof. Cope as to the value of the latter character, to 
which I attached too much importance, I yet wish to uphold 
the distinction of the genera Cyclura and Metopoceros on the 
ground of the cranial structure. Although closely allied to 
Cyclura , Metopoceros is, in some respects, equally related 
to Iguana , whilst the skull of Cyclura stands nearer to that 
of Ctenosaura than to that of Metopoceros. 
On this occasion I propose to indicate the distinctive cranial 
and dental characters of the genera more nearly related to 
Iguana. 
1. Amblyrhynclius , Bell. — All the teeth trilobate. Pre- 
maxillary not extending as far as the posterior border of the 
nasal fosse ; the length of the latter nearly equals their dis- 
tance from the orbits. Prefrontal not entering the nasal 
fossa. Postfronto-squamosal arch short, not longer than the 
orbit ; postfrontal as long as deep. Transpalatine in contact 
with palatine. Basisphenoid short and much constricted 
behind the basipterygoid processes. 
* Proc. Amer. Phil. Soc. xxiii. 1886, p. 261. 
