MYEIAPODS OF NOVA SCOTIA. 235 



ments. The body ordinarily varies from 3.5°^™- to 3.75°"°- in breadtli, but is sometimes 

 so much distorted as to be only 2.25 """• broad. The segments are still more convex 

 than in X. similis Scudd., exceedingly short, and vary in length from .425 ""■ to 

 .675 °"°', averagmg about .58 °™- only ; in other words, the average length of the segments 

 to their breadth is as 1 : 5.617 ; the surface does not present any noticeable irregularities, 

 and neither the anterior nor posterior margins appear to be thickened. 



The frustra are quadrangular in shape, cross the segments regularly and are very nearly 

 square, save at the lower portion of the sides of the body, where they become almost 

 twice as long as broad ; they vary in breadth from .275 """■ to .5 "™' averaging .42 "^^ ; 

 their average breadth is to their length as 1 : 1.353 ; except in so far as they partake of 

 the convexity of the segments, the frustra are flat, but the upper edge of each is very 

 slightly raised above the surflice of the contiguous frustrum. The fine lines which were 

 noticed in X. similis Scudd., are also found in this species (probably they are common to 

 all), and occur invariably on the lower half of the body only ; in distance apart they vary 

 from .038 mm. to .1 °™-, being usually about .075 """•. In one individual, where only one 

 or two segments are preserved, a slight depression, probably a lateral pore, may be seen 

 iir the centre of one of the middle frustra of each segment. Only one specimen, and that 

 a very small fragment, preserves any sign of legs ; they seem to agree in general Avith 

 those of the species previously described, but the different joints cannot be distinguished ; 

 there are apparently two pairs to each segment ; they are 2 °™- in length, and near the 

 base measure from .0625 ""• to .0875 in breadth. 



Xylobius Dawsoni sp. nov. 



The only representatives of this species before me are two admirably preserved single 

 segments and a crushed mass of contiguous segments, all from the middle of the body ; 

 even in the latter case, there are not enough segments to show the form of the body ; 

 the parts preserved measure 23.5 ™°- in length, are comjjosed of about twenty-five 

 segments, and are of uniform breadth throughout, measuring in this direction 3.5 °™- 

 The segments are quite pecuhar, and, if we except then- being broken uito frustra, 

 resemble very closely those of the single species of the genus Archiuhcs, described further 

 on. The portion of the segment lying, in repose, beneath the adjoining anterior segment 

 (I say anterior by assumption, for the remains themselves do not prove anything), is flat, 

 or nearly so — perhaps sUghtly concave ; while the exposed portion is first (anteriorly) 

 strongly and abruptly convex, making a narrow prominent ridge across the bod}^, and 

 occupying a Uttle more than one-fourth of the length of the exposed portion of the seg- 

 ment, and then regularly and broadly, but rather deeply, concave along the remainder of 

 the segment. The segments are longer than in the other species, varying from 1.15 °"°' 

 to 1.65 °"°- in length, and averaging 1.5 ""'•3 but the portion concealed by the over- 

 lappmg of the contiguous segment, .4 mm. in length, is not given in the measurements of 

 the previously mentioned species, and for comparison with them, must be subtracted ; this 

 leaves the average length of the exposed portion 1.1 '^•, and the average length of the 

 segment to its breadth as 1 : 3.4. The exposed sm-face of the segments is provided with a 

 veiy faint, minute and indistinct punctulation ; and also with fine, indistinct lines of scdp- 

 ture, .25 ""• apart, running parallel to each other and to the anterior and posterior borders 

 of the segment. 



