8 BIRDS OF SOUTHWESTERN MEXICO. 



logical Jiorizond of tbe isthmus, we seek what especially distinguishes 

 the western province from that of the Gulf, we will find— 



"I. That it is less remarkable for the number of forms that belong to 

 it than for the absence of others which predominate in the eastern part, 

 to which they give their own physiognomy, and, if I may so express it, 

 one more essentially neotropical. 



" II. That it presents, in relation to the preceding, a marked numerical 

 inferiority in the following families: Turdidce, Tanagrklcc, FringilUdcB, 

 Momotidce, Trogonidce, Ramphastidce, Picidce, Columbidcc, Perdicida;, and 

 Tinamidce. 



"III. That it is remarkable for the almost entire absence of the 

 families DendrocoJaptido), Formicarida;, and Pipridcc. 



" Up to this time, I have only found two native species of Thrushes 

 in the plains of the Pacific. The first, Turdus flavirostris, does not go 

 southeast of the city of Tebuantepec, where it appears at distant 

 intervals, at a period when certain fruits are ripe {Achras, Spondias, 

 &c.) It is probable, as Professor Baird indicates (Review of North 

 American Birds, p. 31), that its center of propagation is in the neighbor- 

 hood of Colima. The second, Miinus gracilis^ is very abundant on the 

 dry plains which extend from Tehuantepec to Tonala. We can give an 

 account, it appears to me, of the numerical inferiority of the Turdidce 

 in the west of the isthmus by considering that Thrushes in general are 

 more especially attached to cold and mountainous countries, and, as it 

 has been seen, the same characteristics do not exist in the isthmus prop- 

 erly so called. Besides, the plains of the Pacific have but a scanty 

 vegetation, formed for the greatest part of leguminous plants, which 

 birds whose natural diet is berries (as for example Planesticus) seek for 

 but little. This latter circumstau^e explains also the absence of several 

 genera of Tanagridw, such as Bhamphocelns, Phanicotliraupis^ Lanio, &c. 

 " Trogon citreolus is the most common Trogon . in the west of the 

 isthmus. It is less sylvicoline than its congeners ; and the yellow color 

 of its iris is not found, to my knowledge, in any other Trogon of Mexico. 

 " Ramphastos carinatus belongs to the eastern part of the isthmus, 

 in the terres chaudes. Aulacorhamplius prasinus is not found, from what 

 I am called upon to believe, in the isthmus proper, but only in the 

 mountainous and temperate parts, which border it on the northwest 

 and southeast. As to Pteroglossus torquatus, I have not found it else- 

 where than at Santa Etigeuia. 



" Momotus mexicanus is the only species of the family that is resident 



