OF CARBONIFEROUS MYRIAPODS. 297 



larger ridges nearer together in ?ome parts of the same cross section than in others, and 

 placing between them only two instead of uniformly three minor ridges. In all the frag- 

 ments 1 have seen there are either two or three (almost universally three) minor ridges 

 between every pair of larger ridges on every part of the same fragment. It is possible 

 that in the slight tapering of the spine two larger ridges coming nearer together compel 

 the union of two adjacent minor ridges and reduce the number to two instead of three, so 

 that in one portion of a spine one may find two and in another three minor ridges between 

 every pair of larger ones ; but this I have not seen, and can only say that while three 

 smaller ridges usually appear in every interspace between adjoining larger ridges, the 

 number is sometimes only two. Otherwise the proportions of these ridges and serrations 

 to each other is very well shown in fig. 2. 



All the specimens found came from the ironstone nodules of Mazon Creek, near Morris 

 Illinois. 



Explanation of Plates. 



plate XXVI. 



[All the figures represent Palaeocampa anthrax.] 



Fig- 1. A spine 3 x ft to show its appearance under an ordinary strong lens, showing an apparently striated 

 surface. Drawn by Katherine Peirson. 



Fig. 2. An oblique view of a fragment of the surface of the spine - , -° 1 -°, showing the serrations 

 of the larger and smaller ridges and their relations to each other; three of the minuter ri Iges should have 

 been shown in every interspace, but in two of them only two are given. Tile figure is schematic. Drawn 

 by J. Henry Blake. 



Fig. 3. A fragment drawn from nature of the shell of a spine 2ja, as seen with a half-inch objective. 

 Drawn by the same. 



Fig. 4 Schematic view of a cross section of the shell of the spine, showing the relations of size and 

 position of the spine, the shell ami the two kin Is of ridges, J- ^--- Drawn by S. H. Scudder. 



Fig. 5. One of the clusters of spines of tig. 8, J. Drawn by Katherine Pierson. 



Fig. 6. One of Mr. Carr's specimens, showing the head, above, '}. Drawn by the same. 



Fig. 7. The other of Mr. Carr's specimens, '/. Drawn by the same. 



Fig. 8. The specimen with legs, found by Mr. Bliss, f. Drawn by the same. 



Fig. 9. The same cluster of spines shown in fig. 5, f. Drawn by the same. 



PLATE XXVII. 



Fig. 1. Trichiuhts nodulosus, \. From the collection of Mr. P. A. Armstrong, No. 7. Drawn by 

 Katherine Peirson. 



Fig. 2. Trichiulus oiHosus, f. From the same collection, No. 18. Drawn by the same. 

 Fig. 3. Trichiulus nodulosus, f. From the same collection, No. 52. Drawn by the same. 

 Fig. 4. Trichiulus ammonitiformis, j. From the same collection, No. 2. Drawn by the same. 



The remaining figures belomr to the next memoir. 



