‘allus. Most of the species of the other sections of On- 
cidium have a short, variously tumid column-base, but 
only the Cucullata types enjoy the horseshoe-like shape 
which shelters part of the callus. Yet, analogous situa- 
tions exist in the Section Stellata, which is a different 
type of modification of the basic pattern. Until we have 
a satisfactory key to the various genera of the Oncidium 
alliance, I decided to maintain this section under 
Oncidium. 
In the past, several Odontoglossum species of the O. 
rigidum relationship have been referred to the Section 
Cucullata because of the connate lateral sepals and the 
sessile sepals and petals. A study of all the characters has 
necessitated the exclusion of these species from the genus 
Oneidium tor the above listed characters document an 
obvious case of parallel evolution rather than similarity 
based on close relationships. Likewise Oneidium Storhki 
and O. Warscewiczi must also be excluded from the 
Section Cucullata due to the different columnar struc- 
tures of the flowers. 
Several noteworthy characters within the section serve 
to distinguish the species. Of the 19 species recorded in 
this paper, ten have a tuft of hairs at the base of the 
elongate callus, while the remainder have a short tumid 
‘allus without hairs. With respect to the calli, three 
species—O. andigenum, O. mimeticum and O. sanguino- 
lentum—have five subglobose tubercles in three rows. 
All others are with three-membered, variously merged, 
tumid or keel-like structures. The familiar long nose-like 
tubercle is found in O. eucullatum, O. olivaceum, O. 
Kennedy and O. rhodostictum; long, sulcate callus which 
is tridenticulate at the apex, on the other hand, is limited 
to O. spathulatum, O. tripterygium and O. Dayanum. 
Five species—O. cucullatum, O. mimeticum, O. oliva- 
ceum, O. rhodostictum and O. sanguinolentum—have a 
