102 



PALEONTOLOGY OF NEW YORK. 



primftry ribl)on; 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 lamellae. 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 lamellae 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 



Fig. 77. 



Approximate determination or the loop in 



Kayseria lens, Phillips. 



FlO. 78. FIO. 79. 



rig. 78. Pexidella Strohmaperi, .Suess. 

 •Fl(t. 70. IHplospirelln Wissmanni, Mtlnster. 



(BiTTNKH.) 



