PLATE LXXI. 



(Figures l-;i (jopies ; i, .), H-XI l)y \l 1'. Wiiiti'ikld ; li-lll. 11-lH, 3-t-as hy G. li. Simpson ; 11-13, n-ii by K. Kmmons). 



Genus BARRANDELLA, gen. nov. 



Page 241. 



Bakkandella linguifera, Sowerby. 



Figs. 1, 2. Dorsiil and inolile views of a normal individual ; showing th« cliai-ai;toi- of the exterior and 



the well defined median fold on the brachial valve. 

 Fig-. 3. A longitudinal median section of the valves ; showing the small sjiondylium and (ixtremely short 

 median septum of the pedicle-valve, and one of the septal plates of the brachial valve. 

 Wenlock limestone. Dudley, Enyland. 



(Figui-es l-,5 after Davidson ) 



Bauuanuella ventkicosa, Hall. 



Figs. 4, 5. Front and dorsal views of a typical example ; showing the fold upon the Virachial valve, its 

 faint plication, and the cavities of the median sejjta. 

 Niagara dolomites. Waukeslia, )Visco'i/^iii. 

 Figs. 6, 7. Ventral and profile views of a ventrico.se specimen \vith a low sinus on the pedii-le-valve. 

 Figs. 8-10. Dorsal, profile and front views of a smaller individual having the fold and sinus distinctly 

 plicate. 



Niagara dolomites. Near Miiwaukee, WiscoTusm. 



Bakkandella foknicata, Hall. 



Figs. 11-13. Profile, dorsal and ventral views of the exterior of a specimen of avei'age size ; showing the 

 median fold on the brachial valve, the single broad plication in the sinus of the pedicle-valve, 

 and the faintej- plication of the latei-al slopes. 

 Clinton group. Lockport, Neio York. 



Bareandklla Areyi, .s[). nov. 



Figs. 14-16. Dorsal, profile and ventral views of a normal example ; showing the strongly plicated fold 

 and sinus on the brachial and jiedicle valves respectively, and the sharp plication of the lateral 

 slopes. X 2. 



Clinton grou]i. Bocliesier, New Y(yrk. 



Bakrandella Barrandii, Billings. 



Figs. 17, 18. Dorsal and ventral views of a large and typically developed individual ; showing the broa<i 

 plication in the median sinus of the pedicle-valve and the corresponding median groove on the 

 o,[jposite valve ; also the finer plication of the medio-lateral region. 

 Figs. 19, 20. Dorsal and profile views of a smaller and more gibbous specimen. 



This species, in its earlier growth stages, is very similar in form and contour to B fornicata 

 (figs. 11-13), but the rapid increase in size of the median plication in the sinus of the pedicle- 

 valve, during the later growth stages of the shell, has the etl'ect of reversing the relative 

 position of fold and sinus in the final condition of growth. 

 Anticosti group. Besde Biver, Anticosti. 



