PLATE 32 I). 

 Fig. 1. 172. 1. Delthyeis lynx. (Pag. 133.) 



1 a, b, c, d. A series ol' specimens, showing the gradations in size, and the increase in number of plications as 

 the shell becomes older. The smaller specimen 1 a has three plaits in the sinus and four on the mesial 

 lobe, witli seven on each side, thus : 7 f 7. In 1 b, there is the partial development of a fourth plica- 

 tion in the sinus, and a fifth on the mesial lobe, though there is no increase in the number of lateral 

 ones. In c and d, there is a full development of the f medial plications, and 10 lateral ones. 



I e and /, are front views of a and d. 1 g. Profile view of d. 



1 h. Ventral valve of another form, showing e.vtended beaks. Medial plications f ; lateral ones 13 on each side. 



1 i. Front view of the same. 



1 k, I, m, 0, q, 4, u. A series of western specimens, with the mesial and lateral plications (7 f 7 ) ; showing 

 DO tendency to increase of either number, though the size of the shell increases as in the previous series. 

 Figures 1 m, q and s, show the cardinal extremities more extended and acute than in the other forms ; 

 while the specimens o and u have the cardinal extremities shorter, scarcely equalling the width of the 

 sheU. 



1 n,i>, r, t, are front views of 1 »i, o, q, u, respectively. 



I A, B. Cardinal and profile views of an extremely globose specimen, having the cardinal line much less tlian 

 the widtli of the shell, and the extremities rounded : the area is broad, and very well defined. The 

 plications are 7^7. 



1 c. Dorsal valve of a specimen, having the cardinal line extended beyond the width of the shell, and ter- 

 minating in short acute ears. 



1 D. Front view of the last, showing the plications, which are 10 f 10. 



1 E. Profile view of the same. 



1 F. Cardinal view of another specimen, with the extremities extending beyond the greatest widtli of the shell 

 below. 



1 G & H. Front view and profile of a specimen similar in form to 1 b, but having the plications 10 ^ 10. The 

 cardinal line is less tlian the width of the shell. 



1 I, K. Front view and ventral valve of a cuboidal specimen, showing some irregularity in the development of 

 the plications ; a single one on the sinus and two on the medial lobe being fully developed, with smaller 

 ones on each side, while the lateral plications are six and seven. 



Tlic following present some deviations from the prevailing forms, and approach to tlie Spirifer denlaius ol ul 

 Verneuil : 



1 L, M, N. Ventral, dor.sal, and profile view of a small specimen, with tlie plications arranged thus : 5 ^ .5. 

 1 o, p, Q. Ventral, front, and profile view, having the same form and proportions a.s the last, but liaviiig an 



additional plication upon each side. 

 1 H, s, T, u. Ventral valve, front, cardinal, and profile views of the same specimen, which is remarkably 



extended on the hinge. This specimen has a single fully developed plication in the sinus and two on the 



mesial lobe, with the rudiment of another on each side of the sinns and of the mesial lobe, while the 



lateral plications are ten on each side. 



