November 4, 1898.] 



SCIENCE. 



615 



H. Adams), which has as one of its charac- 

 ters a more or less completely developed 

 gill. A new genus of the patelliform Lim- 

 nseids, Protaneylus, from the lakes of Celebes 

 differs by the same character from the Pa- 

 Isearctic Ancyhis. The authors suggest that 

 these facts indicate that these forms retain 

 ancient characters belonging to a time 

 when the fresh-water Palmonates were 

 less differentiated from the marine Opis- 

 thobranchiates than at present. Welcome 

 details are also given of the opercula and 

 radula of various Melanians and Viviparidw. 

 There are a few Neritince, two Corbieidce and 

 a species ofBatissa, but one of the curiosities 

 of the Celebes fauna is the absence of 

 Naiades, though the latter occur both east 

 and west of Celebes, in Borneo and Austral- 

 asia. 



Wm. H. Dall. 



AN INSTANCE OF LOCAL TEMPERATURE 

 CONTROL OF THE DISTRIBUTION OF 



3IA3I3IALS. 

 It is a well-known fact that boreal mam- 

 mals, such as lemmings (Synaptomys) , red- 

 backed mice {Evotomys) and long- tailed 

 shrews (Sorex), are found locally in cool sit- 

 uations far to the south of their normal 

 range. The faunal status of the species is 

 thus in no way altered, however ; for the 

 occurrence of an animal beyond its usual 

 geographic limits does not prove that the 

 species can defy the influences of climate. 

 While every life zone undoubtedly has 

 its outlying islands, perhaps the best- 

 known instances of the phenomenon are 

 the small boreal areas scattered through the 

 transition zone and northern part of the 

 upper austral zone in the eastern United 

 States. Many of the ' boreal islands ' 

 are found on mountain tops, where 

 their presence is readily explained by the 

 low temperature of high elevations, but 

 others occur practically at sea level, or 

 at an altitude much below that normally 



attained by the zone in which they lie. 

 Good descriptions of ' islands' of this kind 

 have been recently published by Mr. Ver- 

 non Bailey and Mr. Chas F. Batchelder. 

 Mr. Bailey calls attention to ' Tamarack 

 Swamps as Boreal Islands,'* and mentions 

 the fact that the layer of sphagnum with 

 which these swamps are generally carpeted 

 acts as a cooling agent, partly by protecting 

 the ice which during the winter forms be- 

 neath it, and partly by inducing evapora- 

 tion, by which the air at the surface is con- 

 tinually cooled. He found many ' islands' 

 of this kind in the upper austral zone near 

 Ann Arbor, Michigan. Mr. Batchelder de- 

 scribes the cold rock slides in which the 

 Hudsonian Microtus ehrotorrhinus occurs in 

 the Canadian zone of the Adirondacks, and 

 the swamps that afford the Canadian 

 Evotomys gapperi a congenial home in the 

 transition zone of southern New England. f 

 The so called ' rock vole,' Microtus ehrotor- 

 rhinus was found in Essex County, New 

 York, on " a steep hillside heavily wooded 

 with an old mixed growth. The lower 

 slopes were made up of a talus of large an- 

 gular blocks of rocks piled one upon another 

 as they had fallen from the cliffs above. 

 The damp rocks were covered with sphag- 

 num and ferns, and from the holes and 

 spaces between them came currents of cold 

 air, indicating the presence of masses of yet 

 [August 29] unmelted ice somewhere in the 

 depths below." Oi Evotomys in southeastern 

 New England he says : " One may look 

 for it with some confidence in almost any 

 large tract of wet ground that retains its 

 moisture through the summer, but is not 

 subject to serious floods, and which bears a 

 growth of woods sufficiently heavy to af- 

 ford it dense shade, so that the ground be- 

 neath and the roots of the trees are cov- 

 ered with a deep carpet of sphagnum. * * 



*SciE]SrcE, N. S., III., p. 250, February 14, 1896. 

 tProc. Boston Soo. Nat. Hist., XXVII., pp, 188 

 and 192-193, October, 1896. 



