86 



PALMONTOLOGY OF NEW YORK. 



upward and backward, to form the first volution. The spirals are connected 

 by a loop, which takes its origin on the first hall' of the primary lamellae, the 



FIO. 57. 

 Diagram of the structure of the brachidium in Athyris. 

 X. Spiral coil. s. Saddle. 



a. Primary lanielliB of spiral coil. m. Fimbriated extensions of saddle. 

 a^. Secondary Ianiell<e. t. Stem of loop. 



a". Umbonal blades. f. Arms of loop. 



c. Crura. 6. Accessory lamellae. 



I, Loop. n. Fimbria on outer margins of lamellae, 

 c. Latf^ral branches nf loop. 



two lateral lamellae converging, and uniting at about half the distance across 

 the base of the cones, to form a broad saddle with a convex upper surface ; the 

 anterior extremity of this saddle may be simple or divided ; its posterior por- 

 tion is narrowed, inclined downward or toward the beak of the brachial valve 

 for a short distance, thence it rises abruptly toward the umbo of the pedicle- 

 valve, and bifurcates near the extremities of the crura, each branch following 

 the curvature of the primary lamellae and continuing for only a part of the dis- 

 tance between the ends of the crura and the origin of the loop. These acces- 

 sory lamellae vary somewhat in form, are narrower than the ribbon of the coil, 

 and lie between the primary, and the first band of the secondary lamellae. 





> 







'/ v^ 







o 



sy'' 



Fig. 68. yiQ 59 



Fig. 5S. Vertical section of Athyris mbUlita, Hall, just back of the loop ; showing the crura (c) and the accessory 



Fig. 59. Vertical section of Athyris subtilita, Hall, through the stem of the loop. This view shows the great width 

 01 the primary lamella), the inclination of the accessory lamella (a, a) to them, and the thickened inner 

 edges of the secondary lamellaj. (Cj 



