674 



SCIENCE 



[N. S. Vol. XXVI. No. 672 



inated in the same general region as that in 

 which they now occur. Dr. ~R. P. Whitfield 

 has published^ accounts of a number of species 

 of Uiiio, in the old broad sense, which have 

 been obtained in the Laramie beds of Mon- 

 tana, and has called attention to their great 

 resemblances to some of the more character- 

 istic forms of the Mississippi and Ohio val- 

 leys. Placing these in their modern genera 

 we find: 



Unio gibhosoides Whitf. resembles gibhosus 

 Barnes. 



Pleuroiema wsopiformis (Whitf.) resembles 

 cesopus Green. 



Ohliquaria letsoni (Whitf.) resembles cor- 

 nuta Barnes. 



Quadrula cylindricoides (Whitf.) resembles 

 cylindrica Say. 



Quadrula pyra-midatoides (Whitf.) re- 

 sembles pyramidata Lea. 



Quadrula verrucosiformis (Whitf.) re- 

 sembles verrucosa Barnes. 



Ohovaria retusoides (Whitf.) resembles 

 retusa Lam. 



Thus several genera are represented, and as 

 to the species, Dr. Whitfield says " some of 

 them are so nearly like the living species, that 

 it would do but little violence to specific fea- 

 tures to state that they were the same." In 

 view of these facts he adds : " I venture to 

 state that these further western waters of the 

 Laramie times were, the original home of 

 much of the Unio fauna of these [Mississippi 

 and Ohio valleys] more eastern recent locali- 

 ties." 



AN ANCIENT TYPE OP TREE 



The Ginkgo, now commonly planted in the 

 states along the Atlantic coast, is of interest 

 to all botanists on account of its curious foli- 

 age, and especially because it is the last sur- 

 viving member of a very ancient and at one 

 time widespread genus. Miss M. 0. Stopes, 

 in a description of the flora of the Inferior 

 Oolite of Brora, Scotland," points out that 

 the Ginhgo digit ata (Brongn.) of those beds 

 is so like some examples of the living G. 



' Bull. Amer. Mus. Nat. Hist., XIX., and espe- 

 cially XXVI. (1907). 



' Quart. Journ. Oeol. Soc, August 14, 1907. 



hiloha that at first sight no difference can be 

 observed. However, by great good fortune the 

 epidermis of some of the specimens of G. 

 digitata is well preserved, and shows cells 

 with even outlines, whereas in hiloha the out- 

 lines of the cells are mostly wavy, the differ- 

 ence being considered of specific value. 



HYBRID HUMMING BIRDS 



Messrs. John E. Thayer and Outram 

 Bangs have lately published' a short paper on 

 hybrid humming birds, of which four are now 

 known from California alone. These, occur- 

 ring, of course, in the wild state, are all be- 

 tween different genera; but the genera in this 

 group are many of them very closely allied. 

 The fact and character of the hybridization in 

 each case is determined wholly from a study 

 of the skin, but the authors seem confident 

 of their results. The presumed hybrids are: 



Selasphorus alleni X Calypte anna. 



Trocliilus alexandri X Calypte anna. 



Trochilus alexandri X Calypte costw. 



Selasphorus rufus X Atthis calliope. 



crested titmouse hybrids 

 BoBolophus hicolor, the tufted titmouse, 

 ranges from the Atlantic coast to the Great 

 Plains. B. airicristatus, the black-crested tit- 

 mouse, ranges from the highlands of Vera 

 Cruz to central Texas. At the line of junc- 

 tion of the humid and arid divisions of Texas 

 these birds meet one another, and all sorts of 

 intergrades occur. Dr. J. A. Allen has made 

 an elaborate study' of these Texas forms, 

 based on more than 200 skins, and arrives at 

 the conclusion that it is a case of hybridiza- 

 tion, not of geographical gradation. " The 

 same localities furnish, at several known and 

 quite widely separated points, birds of pure 

 blood of both species, and intergrades having- 

 almost every possible combination of the 

 strikingly dissimilar features of the two spe- 

 cies." There is a genuine geographical varia- 

 tion in size observable in both species; the 

 larger northern race of B. airicristatus is 



' The Auk, July, 1907, p. 312. 

 '^ Bull. Amer. Mus. Nat. Hist., XXIII., separates 

 dated June 12, 1907. 



