48 BULLETIN 168, UNITED STATES NATIONAL MUSEUM 



mucrones — all enable the furcula to take advantage of the resistance 

 of the surface film. This species is exceptionally tolerant of cold, 

 being active in February or March in Massachusetts on days when 

 the temperature is that of winter rather than spring. Krausbauer 

 found specimens in Germany among moist leaves on the shore of a 

 stream under ice at a temperature of —10° or —11° C. 



In Massachusetts, partly grown individuals were common in 

 February, but by April most of the specimens were full grown. 



Dist7'ibution.— Recorded as follows: 



Massachusetts: Arlington, February 21, March 1, 10, April 13. Brookline, 

 April 11, R. W. Hall. Waverley, April 19, 21. 



New York: Voorheesville, November 9, M. D. Leonard (New York State 

 Museum). 



Illinois: Harrisburg, March 6, T. H. Frison and H. H. Ross (Illinois State 

 Natural History Survey). Herod, March 6, T. H. Frison and H. H. Ross 

 (Illinois State Natural History Survey). Mermet, March 8, T. H. Frison 

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



PROISOTOMA (PROISOTOMA) COMMUNA (MacGUIivray) 



Plate 17, Figures 177-180 



Isotoma communa MacGillivray, 1896, p. 50. 



Desc7'iytion. — Blackish blue in alcohol. Head with large pale 

 rounded or elongate spots. First three antennal segments whitish 

 basally, blue apically; fourth segment dark blue. Legs white, tinged 

 with blue basally. Manubrium blue above; dentes white. Eyes 

 (pi. 17, fig. 177) eight on each side, equal, on black spots. Post- 

 antennal organ (pi. 17, fig. 177) near eyes, elliptical, about three times 

 as long as the diameter of an eye. Antennae longer than the head 

 (as 7:5); segments stout, as 10:18:16:27; second and third segments 

 clavate. Sense organ of third antennal segment (pi. 17, fig, 178) 

 with a pair of stout, subcylindrical, slightly curving sense rods, ap- 

 parently without a basal ridge. Tibiotarsus not subsegmented. 

 Unguis (pi. 17, fig. 179) with a pair of strong lateral teeth, without 

 an inner tooth. Unguiculus relatively large, extending three-fourths 

 as far as the unguis, broadly lanceolate, untoothed, with a pair of 

 inner lamellae, - Tenent hairs absent. Third abdominal segment 

 longer than the fourth (as 5:4). Genital and anal segments not 

 ankylosed. Furcula appended to the fifth abdominal segment, ex- 

 tending to the ventral tube. Manubrium slender, with many dorsal 

 and ventral setae. Dens twice as long as the manubrium, slender, 

 tapering, with many dorsal and ventral setae, and with large dorsal 

 tubercles except apically. Mucro (pi. 17, fig. 180) stout, with 

 strongly rounded ventral contour in lateral aspect, quadridentate; all 

 the teeth being dorsal. First and second teeth subequal. Third and 

 fourth teeth almost opposite each other, the lateral tooth being 

 shghtly oblique and either more proximal or more distal than the 



