86 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



Ohio: Salineville, February 17, 19, December 21, 25, A. D. MacGillivraj' 



(Museum of Comparative Zoology, Cornell University). 

 Illinois: Homer, April 29. Urbana, March 11, 13, April 5. Oregon, April 3, 



T. H. Frison and H. H. Ross (Illinois State Natural History Survey). 



ISOTOMA (VERTAGOPUS) ARBOREA (Linnaeus) variety NIGRA MacGillivray 



Plate 28, Figures 316-319 



Isoloma brunnea MacGillivray, 1896, p. 52. 

 Isoioma speciosa MacGillivray, 1896, p. 55. 

 Isotoma nigra MacGillivray, 1896, p. 56. 



Description. — This variety differs from typical arborca only in 

 having no knobbed tenent hairs; in place of these there being a single 

 long simple hair. The color is blackish purple, with legs and furcula 

 whitish, yellowish, or brownish. In this variety, as in the typical 

 form also, the lateral tooth of the mucro may be reduced to a rounded 

 Imob (pi. 28, fig. 316). 



Remarks. — My figures of nigra (pi. 28, figs. 316-319) would answer 

 equally for typical arborea. 



MacGillivray's brunnea, speciosa, and nigra are this variety. 

 Except in lacking tenent hairs, his cotypes of these agree exactly with 

 his cotypes of terminata and synonymica (synonyms of arborea); the 

 slight differences given in the original descriptions being all within 

 the range of individual variation of the species. /. brunnea, for 

 example, has a blunt apical mucronal tooth and no lateral tooth (one 

 cotype in Museum of Comparative Zoology; one from MacGillivray). 

 /. speciosa has the lateral mucronal tooth absent in one cotype but 

 present in another (one cotype. Museum of Comparative Zoology; 

 one from A. P. Morse). Of nigra, I studied four cotypes (two in 

 Museum of Comparative Zoology; one from A. P. Morse). 



To designate this variety I have retained MacGillivray's name of 

 nigra, preferring this for the reason that the descriptions of brunnea 

 and speciosa were based on abnormal individuals. 



The variety nigra may be found intermingled with the typical 

 arborea. Thus, in two collections that I made under the loose bark 

 of one log (Urbana, III., March 11, 13) both forms were present; and 

 a vial of many specimens from F. L. Harvey (Orono, Maine, March 10, 

 in moss) also contained both forms. On the other hand, nigra may 

 occur b}^ itself. Charles Macnamara, of Arnprior, Ontario, used to 

 take nigra every winter on the snow, without ever finding typical 

 arborea. 



Distribution. — Recorded as follows: 

 Maine: Orono, March 10, April, October 28, F. L. Harvey. 

 Massachusetts: Arlington, March 20. 



New York: Altamont, April 12, C. R. Crosby and S. C. Bishop (New York State 

 Museum). Ithaca, March 20, 25, A. D. MacGillivray (Cornell University). 

 Rochester, April 9, November 16, E. A. Maynard. Varna, November 

 (Cornell University). 

 Ohio: Salineville, A. D. MacGillivray (Museum of Comparative Zoology). 



