86 
PALEONTOLOGY 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 half of the primary lamellae, the 
a 
Fig. 57. 
Diagram of the structure of the brachidium in Athyris. 
X. Spiral coil. s. Saddle. 
a. Primary lamellse of spiral coil. m. Fimbriated extensions of saddle. 
a'. Secondary lamellae. t. Stem of loop. 
a". Uinbonal blades. f. Arms of loop, 
c. Crura. 6. Accessory lamellae. \ 
1. Loop. n. Fimbria on outer margins of lamellae, 
e. Lateral branches of 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. 
Fig. 58. Fig. 59. 
Fig. 58. Vertical section of Athyris suhtilita, Hall, just back of the loop ; showing the crura (c) and the accessory 
lamelliB (a). 
Fig. 69. Vertical section of Athyris suhtilita. Hall, through the stem of the loop. This view shows the great width 
of the primary lamellie, the inciination of the accessory iameilse [a, a) to them, and the thickened inner 
edges of the secondary iamelias. (C.) 
