.--The relationships among the American sharp-tailed grassland sparrows currentiy placed in the eenera Passerculus, Ammodramus, Passerherbulus, Ammospiza, and Myospiza are often dis- cussed by ornitho!oeists, but the literature contains little to enlighten these relation- ships. Generic splitting was carried to the extreme by 0berholser, who maintained a distinct genus for virtually every species in the complex. His rationale for this position was that "the only other consistent course seems to be to merge Fasserherbu!us with Ammodramus and Centronyx, for the differences that separate these genera from Passerherbdus are no more important than the structural differences between the species of Passerherblus itself" (Ohio J. Sci., 17: 332, 1917). R. Ridgway (A manual o! North Am. erican birds, Philadelphia, J. B. Lippincott Co., 1887) originally placed all the sharp-tailed grassland sparrows in the genus Ammodramus. More recently R. S. Palmer (Bull. Mus. Comp. Zool., 102: 550, 1949) combined Ammodramus and Passercul.us without explanation, but erred in using the latter, more recent name for the combined enus; he continued to recognize Ammospiza as a separate genus. A. R. Phillips, J. Marshall, and G. Monson (The birds o! Arizona Tucson, Univ. Arizona Press, 1964) also without explanation use Ammodramus for all Arizona species of this group of sparrows. Figure 1. Dorsal view of juvenile sparrows. From reft to right: Passerculus sand- wichensis, Passerculus sandwichensis >( Ammodramus savannarum, and Ammodramus Figure 2. Ventral view of juvenile sparrows; same order as in Figure 1. An indication of the close relationship between distinctive types among the grass- land nesting sparrows is a hybrid between the Grasshopper Sparrow (passerculus sandwichends) and the Savannah Sparrow (Ammodramus savannarum) I collected at the north end of Lago Texcoco, Valley of Mexico, 19 July 1957. The hybrid, a female in slightly worn juvenal plumage, wei-ed 16.4 g and showed no apparent structural abnormalities. In general coloration and dorsal pattern (Figure 1), the hybrid is most similar to a comparable juvenile P. sandwichends. Ventrally (Figure 2) its most striking feature is the same as that of the Zonotrichia and Melospiza hybrid (Dickerman, Auk, 78: 629, 1961; see Figure 2), the near absence of the breast streakings so characteristic of the juvenal plumages of both parental types. Five juvenile A. savannarum at hand from Idaho and Minnesota show much variation in the extent and darkness of these streakings; one bird has them greatly reduced. but not to the extent shown by the hybrid. The few streaks present in the hybrid show a tinge of rust, a color com- pletely absent in the juvenile P. sandwichends but characteristic of A. savannarum. The sides and flanks are unstreaked as in the A. savannarum juvenile (Figure 3); the moustache mark is well developed as in juvenile P. sandwichensis, but the auricular area is pale as in A. savannarum. The hybrid has streaked rather than sealloped interscapular feathers, giving the general aspect of P. sandwichends, but the nape feathers and those of the posterior Figure 3. Lateral Sew of juvenile sparrows: same order as in Fixture 1. portion of the crown are lightly scalloped. With all but the napes covered, one can not distinguish between the hybrid and the A. savannarum young in Figure 1 (allow- ing for greater compression in the nape region of the latter resulting from make of skin). The upper tall coverts are relatively lon as in the P. sandwichensis juveniles. They repeat the rust color found in the breast streaking and in the greater secondary coverts reminiscent of the way in which rust color dominates these areas in the basic plumage of A. savannartm. The edgings of the secondaries and tertials are richly colored as in P. sandwichensis. The tertials are long, similar to those of P. sand- wichensls. The wing is short, closer to A. savannarum. The rectrices are similar to those of P. sandwichensis in shape and are dark; the central feathers are without the pattern found in A. savannarum. The outermost right rectrix (the outer left is missing) is whitish on the exterior edges of both vanes at the tip as in A. savannarum. The tail is somewhat more graduated as in the latter species and is intermediate in length between those of the few jurehals of each species at hand. The bill is small as in the Mexican plateau populations of P. sandwichenis. Soft parts were not recorded, but the bill in the dried skin is darker, resembling young P. sandwichensis. Four young A. savannarum at hand have much paler mandibles and slightly paler maxillae than three P. sandwichensis or the hybrid. There seems to be no consistent difference in the colors of the dried tarsi and toes of the juveniles. No Grasshopper Sparrow specimens have been taken from the Valley of Mexico during the breeding season, and the present hybrid is the first indication of such a population. The type locality of A. s. bimaculatus is Temascaltepec, State of Mexico, only about 85 miles west-southwestward from Mexico City. At the time this speci- men was collected in 1957, the north end of the Lago Texcoco was rapidly being drained and plowed. The last marsh vegetation of that portion of the lake was de- stroyed the following year (Dickerman, Occ. Pap., Univ. Minnesota Mus. Nat. Hist., no. 9, 1962; p. 21). Thus while the area was highly suitable for Savannah Sparrows, most of the lusher grasses and sedges had already disappeared and one would not have expected Grasshopper Sparrows in the area. Today the only suitable places where the species might breed in the Valley of Mexico are near the Mexico City Airport where sewage drainage maintains some marsh areas, possibly around two duck preserves on the west side of the Valley near the town of Atenco, or in the vicinity of Lago Zumpango. The author wishes to thank the curators of the following collections for permitting him to examine material in their care. American Museum of Natural History; Car- negie Museum, Pittsburgh; Museum of Vertebrate Zoology, University of California. Berkeley; United States National Museum. Allan R. Phillips's collection was ex- tensively used in the latter stages of this study. The hybrid is deposited at the Uni- versity of Minnesota, Museum of Natural History. Collecting in Mexico was done under permit from the Departmento de Conservacion de la Fauna Silvestre.--RoBERT W. DCKERM^, Department of Microbiology, Cornell University Medical College, New York, New York.