PLATE XXIX. 



PAGE. 



Figs. 1 to 4. LINGULA ELDERI Whitfleld ... 339 



1 . Dorsal view of an exfoliated specimen to show the flattening along the lateral 

 margins. Trenton limestone, Minneapolis, Minn. Minnesota Geological Sur- 

 vey collection. 



Interior of the ventral valve, drawn from a natural cast, the usual mode of 

 occurrence of this species. (/, umbonal scar; 7i, central scars; fc, middle laterals; 

 ji, anterior lateral and transmedian scars; v, vascular sinuses; vs, vascular 

 trunks. (After Whitflald.) 



View of the interior of the dorsal valve taken from a natural cast, j, anterior 

 lateral scars; lik, lateral, transmedian and middle lateral scars; other letters 

 as above. (After Whitfleld.) 



Profile outline, to show the relative convexity of valves and the great elevation 

 of the ventral beak. Trenton limestone, Fountain, Minn. Collection of C. 

 Schuchert. 



Figs. 5 and 6. LINGULA EVA Billings 341 



5. A dorsal valve with strong radiating lines in the anterior half. 



6. Profile outline of the same specimen. Trenton shales, Fremont, Winona county, 



Minn. Minnesota Geological Survey collection. 



Figs. 7 and 8. LINGULA PHILOMELA Billings 342 



A view of one side of the only specimen seen and a profile outline of the same. 

 Base of Hudson River group, near Granger, Minnesota. Minnesota Geological 

 Survey collection. 



Fig. 9. LINGULA BICINIFOKMIS Hall 343 



Ventral valve, showing the rounded Obolella stage of growth in the posterior 

 portion. Trenton shales, St. Paul. Minn. University of Minnesota collection. 



Figs. 10 and 11. LINGULA KICINIFOKMIS, var. GALENENSIS W. and S 344 



View of the ventral valve and profile outline of the same. Galena shales, near 

 Kenyon, Minn. Collection of W. H. Scofleld. 



Fig. 12. LINGULA COBOURGENSIS Billings (?) 346 



View of a specimen provisionally referred to this species. Trenton limestone, 

 Chatfield, Minn. Minnesota Geological Survey collection. 



Figs. 13 and 14. LINGULA (GLOSSINA) HUKLBUTI N. H. Winchell 347 



13. A view of the ventral (?) valve of the type specimen. 



14. Enlarged view of the concentric surface striiB, x 24. Middle Galena, Mantorville, 



Minn. Minnesota Geological Survey collection. 



Figs. 15 to 18. LINGULA (.GLOSSINA) DEFLECTA W. and S 348 



15 and 16. A dorsal valve and profile outline of the same. Galena shales, near Fountain, 

 Minn. 



17. Natural cast of the interior of the dorsal valve, showing the striated internal 



cardinal area, the vascular trunks and sinuses which apparently surround the 

 anterior and lateral muscular scars. 



18. Natural cast of the ventral valve of the same specimen, preserving the markings 



of the muscles and vascular system. Hudson River group, Spring Valley, Minn. 

 Collection of C. Schuchert. 



Figs. 19 to 22. LINGULA IOWENSIS Owen 349 



19. A dorsal valve with the shell broken along the median line, which is due in great 



part to the decomposition of the shell forming the internal septum. The pro- 

 jecting cardinal area of the ventral valve is also shown. 



20. Profile outline of the same specimen. Galena limestone, near Hader, Minn. 



Collection of W. H. Scofleld. 



21. An internal view of the dorsal valve, taken from a gutta percha impression. 



h, central scars; s, septum; x, concentric laterals. (After Hall.) 



22. Natural cast of the ventral valve of the specimen from which figure 21 was taken, 



showing the slightly elevated muscular scars and median septum. Galena 

 limestone, near Fountain, Minn. Collection of C. Schuchert. 



Figs. 23 and 24. SIPHONOTKETA (?) MINNESOTENSIS Hall 358 



23. View from the dorsal side of a specimen retaining the valves in juxtaposition 



and preserving most of the epidermal layer of the shell. 



24. The ventral valve of the same specimen, imperfect in the umbonal region. (After 



Hall.) Trenton limestone at Minneapolis, Minn. Collection of C. Schuchert. 



