WOODWARD HIPPURITID.E. 



51 



the margin ; not branching or communicating with the outer surface, 

 as in Hippurites, but opening round the inner edge of the valve. 



Figs. 19, 20. — External views o/" Bi-radiolites and Monopleura. 

 Fig. 19. Fig. 20. 



Fig. 19. 



I, posi- 



Upper valve of Biradiolites canaliculatus, D'Orb. (f nat. size) : 

 tion of ligamental line ; a, a, areas bordering ligamental groove. 

 Fig. 20. Upper and lower valves of Monopleura imbricata, Math. (^ nat. size) : 

 /, ligamental groove ; p, point of attachment. 

 The genus Monopleura, Matheron, merged in Caprotina by M. D'Orbigny, ap- 

 pears to want the essential features of the latter genus, and at present we have no 

 means of determining whether it belongs even to the same family. The following 

 species may be referred to this provisional genus : M. trilobata and lamellosa 

 (D'Orb.), M. gryphoides, varians, sulcata, imbricata, and Marticensis (Matheron), 

 M. Texana and triquetra (Roemer). 



Figs. 21, 22. — Interior and Exterior o/Caprina. 

 Fig. 21. Fig. 22. 



I 



Fig. 21. Caprina Aguilloni, D'Orb. Interior of left valve : a, a', position of ad- 

 ductors ; I, ligamental groove ; u, umbonal cavity ; t, tooth of fixed 

 valve, broken off and remaining in its socket. 



Fig. 22. C. adversa (after D'Orb.) : c, point of attachment. 



The single tooth of the lower valve is sometimes enormously de- 

 veloped (fig. 21, t). The upper valve is convex or spiral. The 

 cartilage is lodged in a shallow groove or in numerous deep pits. 



E 2 



