384 



THE AMERICAN NATURALIST [Vol. XL 



only 6 and that consequently its sacral vertebrae are much moFe ante- 

 rior in position than has heretofore been supposed. 



G. H. P. 



Adaptations in the Arteries of the Horse. Earner {Jen. Zeitschr. f. 

 Naturw., vol. 40, pp. 319-382) in a study of the thoracic and abdom- 

 inal arteries of the horse has shown that the structure of the arteries 

 varies with the blood pressure, the mechanical relations to the sur- 

 roundings, and the functional relations of the vessels. As the blood 

 pressure decreases in the more distant vessels the arterial walls become 

 thinner and take on more the character of muscular tubes. Where 

 arteries receive support from surrounding parts, as for instance where 

 the aorta pierces the diaphragm, their walls are thin. Finally adap- 

 tations are to be seen where special conditions exist; thus the vertebral 

 artery has its elastic elements unusually developed in relation to a 

 demand for the utmost freedom of movement in the horse's neck. 



G. H. P. 



Two New Chipmunks. Dr. C. H. Merriam (Proc. Biol. Sac. 

 Wash., June, 1905) describes two new chipmunks of unusual 

 interest. One of them, called Eutamias amcenus operarius, is the 

 common little four-striped species of the Boreal zone in Colorado. 

 It has been referred to Say's E. quadrivittatus, but that species lives 

 in the foothills, and the mountain form is actually nearest to E. amcenus 

 •of the Californian Sierras. In view of the widely severed habitats of 

 the forms operarius and amcenus, and the absence of any evidence of 

 intergradation, it would seem that the Colorado animal should rather 

 rank as a full species, Eutamias operarius. The other new chipmunk 

 is E. hopiensis, an unusually handsome form from the Painted Desert, 

 Arizona. T. D. A. C. 



The Ant Genus Liometopum. Dr. W. M. Wheeler (Bull. Amer. 

 Mus. Nat. Hist., Nov., 1905), gives an interesting revision of the genus 

 Liometopum, as found in North America, with a discussion of the 

 habits of the species. The geographical distribution of Liometopum 

 is of especial interest, as it is one of those types which may be desig- 

 nated palaeoboreal; that is to say, it appears to have had a 'boreal 

 distribution in times past, but has now been driven south, where it 

 persists, with few representatives, in the southern parts of the temper- 

 ate zones of both hemispheres. Herein it reminds one somewhat of 

 the butterfly genus Parnassius, but it differs from that in the smaller 



