BRACHIOPODA. 



89 



absent, probably from abrasion, on the earlier portions of the shell, and, 



as already observed, are frequently entirely lost. 

 {c) The hinge-plate is triangular, flat rather than concave in the middle, and 



without post-lateral expansions; it is, moreover, not elevated above 



the plane of the margins of the valve. 

 {(l) The union of the primary lamellae with the crura is more or less obtuse, 



the former making a curve upward, away from the crura, passing them 



again near the hinge-plate ; thus appearing to make a noose on each 



side at their origin.* 

 (e) The loop is very long, its origin from the primary lamellae being at or in 



front of the middle of their length. 



Fig. 60. Fig. 61. 



The crura and loop of Athyris spiriferoides, Eaton. 



(C.) 



(/) The saddle of the loop is broad and undivided at its anterior extremity. 

 (g) The arms, or accessory lamella of the loop, are narrow. 

 {h) The saddle, accessory lamellse and spiral bands are without spinules or 

 fimbria. 



Fig. 63. 

 The crura and loop of Athyris vittata, Hall. 



Fig. 63. 



(c.) 



Of American species which are referable to this typical division of Athvris, 

 may be cited: A. spiriferoides, Eaton, of the Corniferous limestone and Hamilton 



* This peculiar structure was first shown by Mr. R. P. Whitfield, for the species of A. vittata, Hall, 

 and A. spiriferoides, Eaton, in Volume IV of the Palsontology of New York. 



