112 



CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



The shell is marked with distinct cross striae of growth, 

 with fine sharp crenulations, which show only toward ma- 

 turity. The elevations between the pits of the crenulations 

 become in the adult indistinct spiral ridges, giving a finely 

 reticulated aspect to the surface. The cross stride and 

 spiral ridges are not visible on the cast. In the adult stage 

 the surface is ornamented with undulating growth bands, 

 forming weak ribs strongest near the umbilicus and distinctly 

 visible on the cast. These originate from bundling of the 

 cross strige at the umbilicus, and give the shell a decided 

 resemblance to the Triassic genus yuvavttes, which may 

 very possibly be a descendant of Glyphioceras. This bun- 

 dling begins at about 2.3 mm. diameter. 



The visible sutures consist of a pair of pointed ventral 

 lobes (divided by a notched saddle) and a pair of angular 

 lateral lobes. All the lobes and the first pair of lateral sad- 

 dles are angular in the adult, while the second pair of sad- 

 dles is broadly rounded. A second pair of lateral lobes is 

 on the umbilical shoulders, just concealed by the involution. 

 The internal sutures consist of a pointed antisiphonal or 

 dorsal lobe, and a pair of similar lateral lobes. In the early 

 part of the adult stage the lateral saddles are rounded, as 

 shown on PL XV, fig. 11, on a specimen of 15 mm. diam- 

 eter. In the youthful stages all the saddles are broad and 

 the lobes only slightly pointed. 



Measurement of Specimens of Adult Age. 



Diameter 



Height of last whorl 



Height of last whorl from the preceding. 



Width of last whorl 



Involution 



Width of umbilicus 



mm. 



15.00 



7-25 



4.00 



12.00 



3-25 

 1.70 



mm. 



20.7 



8.2 



4.0 



15-7 

 4.2 



mm. 



23.00 

 12.5 



20.5 



7-5 



mm. 



315 

 17.0 



24-5 



