148 S. H. SCUDDER ON SPESTED MYRIAPODS 



There are certain features, however, common to most, at least, of these ancient types, 

 which should he mentioned ; these are the great breadth and depth of the head, which is 

 the more remarkable from the tapering of the anterior extremity. In one or two speci- 

 mens also the antennae have been more or less completely preserved (see PI. 13, figs. 7, 13, 

 18), and appear to differ little from their modern representatives unless it be in their greater 

 slenderness and brevity, possibly resembling more the embryonic condition of modern 

 types. What appear to be eyes are also preserved in one or two instances (PI. 11, fig. 10, 

 and PI. 13, fig. 18), and also present no contrasts worthy of special mention. 



Besides these, careful examination has shown in specimens of not less than four species 

 of two genera, the presence of a long and straight unjointed appendage, or pair of appen- 

 dages, upon the under surface of one of the early segments of the body (the fourth, fifth 

 or sixth), which varies in length from one-half the width of the body to more than its 

 width. It is always entirely different from the spines and clearly not one of the ordinary 

 legs. No other external organ is known in this part of the body in modern Myriapoda, 

 excepting the pair of intromittent organs, which are morphologically legs, supplanting 

 them on the sixth segment, and it seems, therefore, highly probable that we have in these 

 ancient types a movable organ of the same nature, but of an exceedingly simple char- 

 acter. Full description of each instance is given in the text. 



The results reached by a study of these spined myriapods of the Mazon Creek nodules 

 lead naturally to the enquiry what their relations were to other paleozoic myriapods. 

 In some of these previously studied 1 1 have pointed out what I then believed to be for- 

 amina repugnatoria. These are described in Xylobius sig'dlariae Daws., where one spec- 

 imen is said to have " a slight circular depression in the 'centre of one of the frustra 

 . about half way up the sides of the segment; it resembles and is found in the 

 place of the lateral pores." Also in X.fractus Scudd., where " a slight depression, probably 

 a lateral pore, may be seen in the centre of one of the middle frustra of each segment " 

 (only two segments were preserved in this specimen). And also in Archlulus xylobioides 

 Scudd., where they occur " from the seventh segment ... at least to the seventeenth 

 . . . and are placed in the middle of the sides of the segments ; they are oblong oval 

 in shape, with their longer diameters vertical ; the mean of their diameters averaged 0.2 

 mm." in specimens the diameter of whose body is about 4 mm. In a subsequent page of 

 the memoir, mention is made of the " large size " of the lateral pores. 



In lulus Brassi described by Dohrn 2 he says he was unable to find any foramina, but 

 states that Kner thought he had recognized stigmata on some segments above the legs ; 

 " er glaubt an einigen Ringen oberhalb der Beine den Abdruck von Stigmen zu erkennen ; 

 gewisse Punkte," adds Dohrn, " an diesen Stellen kann man gewiss dafiir ansehen, wenn 

 schon ihre wirkliche Natur nicht zweifellos festzustellen ist". 



Woodward in his description 3 of the British Xylobius sigiUariae(X.Woodwardi Scudd.) 

 says : " each segment of the body, wherever sufficiently well preserved to show it, bears 

 upon its lateral portion a slightly raised whart, indicating the position of the pores, stomata 

 or tracheal openings." These are figured in his plate, in fig. 11a, as nearly one-eighth 

 the diameter of the body. 



1 The Carboniferous Mvriapoils preserved in the sigillarian 2 Verb, naturh. Ver. Rheinl., [3], v, 535-53G, taf. 6. 



stumps of Nova Scotia. Mem. Bost. Soc. Nat. Hist., Vol. in 'Trans. Geol. Soc. Glasgow, n, 236, pi. 3 (1867). 



pt. 2, No. 3 (1873). 



