PLATE XXVI. 



(Figures 1-7, 9-11 by R. 1». Whitfield; 8 by F. B. Meek; 12 by E. Emmons.) 



Legend: A. Cardinal area. T'. Internal cast of tube. 

 A. Delthyriiim. j. Cardinal process. 



Dg. Deltidial grooves. b. Dental sockets. 



s'. Transverse delthyrial plate. r. Didiietor scars. 



T. Tubulai- portion of plate. a. Adductor scars. 



Genus CYKTIA, Dalman. 



Page 40. 



Cyrtia alta, Hall. 



Fig-. 1. The internal cast of the brachial valve ; showing- the striated cardinal area, structui-e of the artic- 

 ulating apparatus and the faint plications on the inedi.in fold. 



Fig. 2. The front view of an internal cast of the pedicle- valve; showing the muscular area and the faintly 

 plicated sinus. 



Fig. 3. An exterior view of the cardinal area of the pedicle valve ; showing the concave plate filling the 

 upper part of the delthyrium. 



Fig. 4. A cardinal view of an internal cast of the pedicle-valve ; showing the impi-ession left by the 

 thickened inner wall of the delthyrial plate. 



Fig. 5. A portion of an internal cast of a small brachial valve retaining traces of the muscular sears. 

 Chemung gi-oup. Meadville, Penn. 



Genus SYRINGOTHYRIS, A. Winchell. 



Page 47. 



Syringothyris typa, a. Winchell. 



Fig. 6. The apical portion of a pedicle- valve ; showing the dental plates, the delthyrial plate, with the 



central tubular portion projecting beyond its broken margin. 

 Fig. 7. The opposite side of the same specimen ; showing the extension of the canaliferous tube which is 



slit along its inner surface. 

 Fig. 10. The interior of the umlxmal portion of the pedicle- valve; showing the greatly thickened tubulai- 



or canaliferous plate, not closed along its inner surface. 

 Burlington limestone. Burlington, Iowa. 



Syringothyris subcuspidatus, Hall. 



Fig. 8. A cardinal view of the original specimen. 



Keokuk limestone. Keokuk, Iowa. 

 Fig. 11. The interior of a large pedicle-valve ; showing the transverse plate and the extension of the tube. 



Keokuk group. Nauroo, lUinoi.<s. 



Syringothyris texta, Hall. 



Fig. 9. Central cardinal portion of an internal 'cast of the conjoined valves ; showing the impressions of 

 the cardinal process, dental plates and the filling of the tubular portion of the transverse plate. 



Fig. 12. A preparation, showing the elongate spiral brachial supports, the jugal processes and a portion 

 of the crura, (c.) 



Keokuk group. Neio Providence, iTidiaiia. 



