540 Cook : A Synopsis of the 



Seeds with few longitudinal grooves, the surface not polished, 

 grayish ; embryo subapical. 



The generic name alludes to the preference of this palm for the 

 summits of crags and the brows of perpendicular cliffs which abound 

 in the limestone region of the north side of Puerto Rico. 



The tall, slender trunk and other differences between this genus 

 and TJirinax are probably to be interpreted as ecological adapta- 

 tions necessary to enable the present palm to compete with the 

 vegetation which often surrounds its base, and to withstand the 

 winds to which it is commonly exposed. The species of Thrinax 

 and other allied genera, as far as known, have the trunk rigid and 

 columnar, or even enlarged from the base upwards. When grow- 

 ing solitary and exposed they seldom, if ever, attain half the height 

 of Thrincoma. Usually, however, they are protected by other 

 vegetation or by growing gregariously in thickets. 



Thrincoma might be described as a Thrinax which has adopted 

 habits of the arecoid genus Aeria which grows in similar situations 

 in a neighboring part of the island. In addition to the smooth, 

 slender, and flexible trunk Thrincoma makes further provision 

 against the wind in having fewer, less ample, tougher and more 

 deeply divided leaves and like the arecoid palms it also drops the 

 old leaves as soon as their usefulness is past, instead of retaining, 

 like Tlirinax, a large pendant cluster of them. The details of these 

 differences are given below in a comparative note on fresh material 

 of Thrincoma alta and Thrinax praeceps collected but a short dis- 

 tance apart in the lower part of the Arecibo valley along the 

 Utuado-Arecibo road. In this region of jagged mountains, Thri- 

 nax seeks shelter against the walls of perpendicular precipices, while 

 Thrincoma challenges the wind and the admiration of the traveller 

 by its evident preference for the crags and pinnacles. 



Thrincoma alta sp. nov. 



With but one species known with certainty to belong to the 

 present genus the separation of generic and specific characters 

 would have little purpose. Data for a specific description are, 

 however, contained in the following notes which are retained in 

 their original comparative form as better illustrating the generic 



differentiation of Thrincoma and Thrinax, as represented by 

 Thrinax praeceps. 



