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AKTM CAMBRIAN CONCHOSTRACA — ULRICH AND BASSLER 113 



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 P'lGURES 9,10. Walcottella nitida, new species 37 



9. Light print of photograph of a nearly perfect right 



valve. 



10. Darker print of same showing surface markings 



and rather strong convexity of valve. The com- 

 paratively slight development of the median 

 tubercle, the relative prominence of the ocular 

 node, and the general shape of the valve is sug- 

 gestive of the Ordovician and Silurian genus 

 Isochilina. (9, 10, Bass Canyon.) 

 11, 12. Walcottella pulchella, new species 36 



11. View of left side. 



12. Outline in a dorsal view of a complete carapace. 



The valves gap at the ends and the surface is 

 covered with minute, crowded puuctae. (Bass 

 Canyon.) 



13. Walcottella obsoleta, new species 39 



The type of this species. The specimen is thought to be 

 a right valve. On account of the unusual abrupt- 

 ness of the cardinal and ventral slopes it is believed 

 to have been originally higher, hence less elongate. 

 The median tubercle is barely distinguishable, prac- 

 tically obsolete. (Bass Canyon.) 

 14, 15. Fordilla troyensis Ba,rra.nde 97 



14. A left valve X 6 of a well preserved carapace show- 



ing the exterior markings. 



15. View of an internal cast, X 6. 

 Lower Cambrian: Troy, N. Y. 



16. Modioloides prisca (Walcott) 98 



The type and only specimen, X 6. 

 Lower Cambrian: Whitehall, Washington County, 

 N. Y. 



17. Aluta douvillei Mansuy 61 



The best preserved specimen, X 6, on the slab figured 



by Mansuy. 

 Cambrian: Eastern Yunnan. 



2607—31 8 



