There are anumber of minor morphological characters 
which serve to distinguish Caularthron bicornutum from 
C. bilamellatum. The former is, in general, a much larger 
and more robust plant than the latter and has flowers 
approximately twice as large. This difference is variable, 
and the specimens of Caularthron bicornutum from Brit- 
ish Guiana are notably smaller in habit and flowers than 
those from other parts of the range of the species. 
Caularthron bicornutum may be recognized at once 
through its deeply trilobate lip. The mid-lobe is charac- 
teristically lanceolate or elongate-lanceolate with the api- 
cal portion either long- or short-acuminate. The lateral 
lobes, which are ovate-oblong and either obtuse or sub- 
acute, are usually separated from the mid-lobe by a deep 
sinus. Caularthron bilamellatum, on the contrary, usually 
has an inconspicuously trilobulate or auriculate lip, the 
mid-lobe of which, characteristically triangular-ovate and 
acute, is not separated from the small, auriform lateral 
lobes by a recognizable sinus. ‘To be sure, several collec- 
tions are known from Trinidad which show a somewhat 
intermediate lobation of the lip, and here there may be 
evidence of hybridization. When the available material 
of these two species from their entire geographic ranges 
is taken into consideration, however, the significance of 
the shape of the lip as indicative of a possible evolutionary 
trend may be appreciated. 
A convenient character for separating Caularthron 
bicornutum trom C. bilamellatum—and a character which 
seems to have been overlooked—is found in the peculiar 
notching of the upper margin of the petals of C. becornu- 
tum. This margin, which faces the dorsal sepal, usually 
has one conspicuous notch situated one-third or one-half 
of the distance from the base of the petal. In some of 
the specimens, the notch is sharp and triangular; in 
others, it is less clearly defined. In all cases, however, 
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