430 Field Museum of Natural History — Botany, Vol. II 



13. Cenchrus carolinianus Walt. 



This species* was found only at one spot, that on the south shore of 

 Perez Island near the clumps of Conocarpus at the edge of the Sporo- 

 bolus colony at that point. The species has also been returned from 

 Cozumel Island but not from the Yucatan mainland. 



The species is avevectent through the spiny burs clinging to the 

 webbed feet of the booby. 



14. Cenchrus insularis Scribn. Field Mus. Bot. 2:26. 



This new species is represented by a few plantst on Pajaros Island 

 only. These were all in full ripe fruit. That this is the full representa- 

 tion of so strongly a differentiated species is open to doubt and will so 



C. insularis. 



C. echinatus 



remain until opportunity is had to visit Utowana Cay, where it would 

 seem more than probable that a fuller growth may be found. 



The characters clearly differentiate this species from C. carolinianus 

 as fotmd on Perez Island; in many of its characters it is much nearer 

 C. echinatus as found abundantly on cultivated lands near Izamal, 

 eighty miles inland on the main, and on the rocky plain south of Pro- 

 greso. I am strongly inclined to judge the latter species to be its parent- 

 age. The fruiting characters of the two species are here illustrated 

 in conjunction. The species differ in the size of inflorescence; number 

 and size of the involucres; character of the basal bristles (barbellate in 



*Reported as C. tribuloides L. in Field Mus. Bot. 2 144. 



tThe specimen from Cozumel reported as this species under the description of 

 the type proves to be C. caroUnianus Walt. 



