102 
PALEONTOLOGY OF NEW YORK. 
primary ribbon; it is directed somewhat posteriorly, its lateral elements unit¬ 
ing to form a short saddle which rests upon, and is supported by the most 
elevated part of the median septum. According to Davidson’s preparations 
the loop is continued into an upright simple stem, from the summit of which 
diverge the accessory lamellse. At this point our own preparations do not 
fully corroborate this account, but indicate rather that this upright stem is 
continued completely across the umbonal cavity and comes into contact with 
the opposite valve, resting upon the median ridge of that valve, or with its 
extremity inserted into a groove upon that ridge. 
We further find that the accessory lamellm originate from a posterior eleva¬ 
tion or process arising from the saddle of the 
loop and are given off at points just in front of 
the crural angles. The ribbon of the principal 
spiral cones is comparatively broad, thickened 
on the inner margins, making six or seven 
volutions in a full-grown shell. The accessory 
lamellae are also produced into spirals which though more delicate are composed 
of as many volutions as the principal spirals. At their outset the branches of 
the accessory lamellae pass between the first and second volutions of the princi¬ 
pal ribbon, and the two are intercoiled in this manner for their entire extent. 
Kayseria is thus an athyroid with double spirals and the only species known 
Approximate determination of the loop in 
Kayseria lens, Phillips. 
(C.) 
Fig. 78. 
Fig. 78. Pexidella Strohmayeri, Suess. 
Fig. 79. IHplospirella Wissmanni, Munster. 
(Bittner.) 
