Plate LXIII - 



Fig. 12, . .ARCHIMEDES SWALLOyANUS Hall. .-; .,-. 5>M 



12. Large axis of this species but of the usual form. Natural size. 



Chester, 111. 



Illinois State Museum. 



12 a, 12 6. Two specimens of a form having the shaft straighter than usual. 

 12 c, 12 d. Two vertical sections. 



Chester, 111. 



Illinois State Museum. 



Fig. 13. ARCHIMEDES PEBMINIMUS Ulr _ 572 



The small specimen shown on fig. 11, x6. 



Chester, 111. 



Illinois State Museum. 



Fig. 14. ARCHIMEDES SUBLAXUS Ulr 579 



The type specimen of this species, of the natural size, showing the lax 

 volutions of two axes, one of them sinistral, the other dextral. 

 . Chester, 111. 

 Illinois State Museum. 



Fig. 15. ABCHIMEDES LAXUS Hall 580 



15. Fragment of the axis, showing nearly two complete volutions. 



Litehfleld. Ky. 



E. O. Ulrica's collection. 



The same specimen is the type of Prof. Claypole's Helico: ora archi- 



mediformis. 

 15 a. Another fragment of this species from the same locality and collection. 



Both natural zize. 



