236 S. n. SCUDDER ON THE FOSSIL 



The frustra are not regularly quadrangular, as in all the previous species, but the lines 

 of division in crossmg the segments curve slightly, and divaricate a little as they pass 

 from the anterior border. If these frustra could slide over each other, as the specimens 

 seem to show, the animal could coil itself more readily and completely than the other 

 species of this genus ; the frustra vary in breadth, increasing, in general, in one direction, 

 but whether upwards or downwards, the nature of the remains does not permit us to 

 judge ; in the two separate segments they varied thus : first (visible onl}^ in one) .35 °"°- 

 by .9 °"°;^ second, .35 "^^ to .675 """•, by 1.05 °™- to 1.25 ■"■"■; thu-d, .5 "™- to .875 "■"-, 

 by 1.1 °™- to 1.25 '°'°-; foiu-th, .575 "°'- to .7 ■""-, by 1.25 """■ ; fifth, .5°"°- to .925 '°°'-, 

 by 1.3 '°'"- to 1.5 ""-J sixth, .675 '"■"■ to .9 °""-, by 1.25 °^- to 1.55 ""•; average .59 """• 

 to .815 '"■"■, by 1.14 "^■"- to 1.36 '"'"•, or .7025 '°°'- by 1.25 ■^■. Both edges of the ex- 

 posed portions of the frustra are raised — that which seems to be the upper one 

 to a considerable degree ; so that, besides partakmg of the varyiug contour of the 

 segment, the frustra are slightly and oppositely concave ; the lines dividing the frus- 

 tra rim through the concealed, as weU as through the exposed portion of the segment, 

 but, in the former case, they do not have their edges raised, and the fines of separa- 

 tion are straight, less distmct, and run at right angles to the anterior border of the 

 segments. The concealed portion of the segment is also provided with fine impressed 

 lines crossing it at right angles to the anterior border of the segment; they are 

 placed at an average distance of .075 "™' apart, but every other one is more deeply 

 impressed and conspicuous. Although some of the specimens are remarkably preserved, 

 I have been unable to detect any trace of lateral pores, and no legs can be seen on any 

 of the fragments. The well preserved single segments are probably fi-om the region 

 near the head where lateral pores do not occur. 



The genus Archiuhis has but a single representative among these sigillarian rehcs ; 

 in general appearance it resembles the last mentioned siDecies, and may be called 



Archiulus xylobioides gen. et sp. nor. 



As this species includes some of the best preserved and most completely coiled speci- 

 mens among the fossUs, nearly every part of the body can be seen in a more or less 

 perfect manner. Excepting at the two ends, the body must have been of nearly 

 uniform width throughout ; at about the seventh segment it begins to taper anteriorly, 

 at first gradually, afterwards qmte rapidly, so that the segments adjoinmg the head 

 are scarcely more than half the width of those m the middle of the body ; the head 

 itself appears to be well roimded, and to have no ridge or crest; apparently the body 

 tapers neither so rapidly nor considerably at the posterior end, although the fragments 

 of this part are less perfectly preserved. None of the fossils exliibit all the segments 

 of the body, but vary in length fi?om 7 """■ to 26.5 "™-, and m the number of 

 segments from nine to thirty-three ; probably fuU grown individuals had as many as 

 forty or forty-five segments. The middle of the body varies from 2.5 °™- to 4.5 '""'■ 

 in breadth, averaging 3.4 °^°'- ; in one instance, at a distance of 15 """■ from the head, 



* The shorter measm-ement is the breadth of the frus- are given, the first in every case refers to the same speci- 

 trum, the longer its length ; when two sets of measurements mens. 



