NO. 1867 AMERICAN FERNS CHRISTENSEN 369 



be found to have a similar number of species. In Central America 

 and Mexico together 26 species are found, of which number 16 are 

 found south of Panama, 8 in the West Indies, and 7 thus far not 

 found elsewhere. Only 3 Central American species, viz., D. sancta, 

 D. diplasioides, and D. Sprengelii, are with certainty found east of 

 Jamaica and Haiti. In the West Indies the continental element is 

 strongest in Jamaica, with such species as D. concinna, D. oligo- 

 carpa, D. panamensis, D. rudis, D. cheilanthoides, and D. Thomsoni, 

 which do not occur at all in the smaller islands. It is probable that 

 most of these species are very old, as well in Jamaica as on the con- 

 tinent, but the possibility is not excluded that an exchange of species 

 may have taken place by means of wind-blown spores, or may be 

 taking place today. It will, therefore, always be impossible to decide 

 definitely in what region a species has had its origin, but certainly 

 Jamaica, like the Andine valleys, is an endemic center of a high 

 order. 



D. sancta and D. delicatula seem to be species of insular origin. 

 The occurrence of the former in Guatemala gives us an example of 

 a West Indian element in Central America. Another instance is 

 found in the Central American D. pseudosancta, which has its 

 nearest allies in the West Indies. On the other hand, such species as 

 D. opposita {vera) and D. Sprengelii, both generally dispersed over 

 all the smaller islands, are to me reduced insular, but specifically 

 fixed, forms of species which have had their origin on the continent. 

 More is said as to this in the treatment of these two species below. 



GROUP OF D. OLIGOCARPA 



Smaller species; pinnae seldom more than 10 cm. long by 1.5 cm. 

 broad; tertiary veins 3-10 to a side. Lamina gradually narrowed 

 downwards, with 1-4 pairs of abbreviated pinnas, rarely abruptly at- 

 tenuate. Basal pair of segments not prolonged. 



DRYOPTERIS CONCINNA (Willd.) Kuntze 

 (Revision 271, No. i, Fig. 2.) 



I can not find out under what name Jenman may have described 

 this species, which in its typical forms has been frequently collected 

 in Jamaica in recent years. The species is very distinct in habit and 

 pubescence, and especially in its uniformly setose sporangia. 



Jamaica : Hart 304. Tweedside, rocky bank in the open, 2,000 ft, 

 Maxon 984. Second Breakfast Spring, grassy bank in the open, 2,000 

 ft., Maxon 989a. Shaded edge of Green River, Maxon 1501 (= Under- 



