258 ENTOMOLOGICAL NEWS [XXXI, '2O 



sent for examination, I cf , I 9 returned to him. Type c? 

 in the writer's collection at the Academy of Natural Sciences 

 of Philadelphia. As to the type locality Professor Alfaro 

 wrote, July 22, 1916: 



" Durante la semana santa estuve en el Volcan de Poas y colectado 

 muchas libellulas en el Potrero del Alto, cerca del crater; alii hay un 

 Hotel y junto a los desagiies de la casa me pareci6 distinguir tres especies, 

 lo mismo que en la zanja del Potrero; la especie de mayor tamano no 

 dejaba arrimarse y de la tercera solamente un ejemplar vi; creo pues que 

 mis ejemplares colectados en numero de 40 son cf y 9 de una sola es- 

 pecie ... las libellulas del Volcan de Poas, por ser esa la mayor 

 altura en que he colectado Odonatos: 2600 metres." 



Mr. E. B. Williamson, at my request, has examined a pair 

 of these specimens collected by Prof. Alfaro and independ- 

 ent of any suggestion from me has also reached the conclu- 

 sion that they represent a new species allied to Sympetrum 

 virgula. 



Several features of 5. nigrocreatum described above are of 

 special interest. According to Dr. Ris,* but three species of 

 Sympetrum possess an additional, or supplementary, trans- 

 verse carina on abdominal segment 4: dilatatum Calvert 

 of St. Helena, illotum Hagen and corr upturn Hagen of (chiefly 

 North) America. S. nigrocreatum is clearly closely related 

 to illotum, yet the male, in the majority of specimens exam- 

 ined, lacks this carina, although the female possesses -it 

 distinctly developed. In the male, the appearance is as if 

 the carina had been smoothed out, its site being indicated 

 by a slight difference in the surface of the segment. Whether 

 the presence or absence of such transverse carinae has any 

 correlation with the internal anatomy has not been deter- 

 mined, apparently. 



Assuming that S. illotum is the nearest ally of S. nigro- 

 creatum, the latter is larger and has a greater number of 

 cross-veins (e. g. antenodals) and of cells on its wings. As 

 nigrocreatum inhabits a higher, and presumably cooler, sta- 

 tion than does the Costa Rican illotum, a causal relation is 



*Libellulinen Monographisch bearbeitet. Cat. Coll. Zool. Selys, fasc. 

 XIII, pp. 617-624, 1911. 



