JURASSIC AMMONITES FROM ECHIZEN & NAGATO. L3 



and umbilical wall perpendicular, ornamented with thickly set, 

 obtu.-c sigmoidal riba separated by valleys mostly narrower, and 

 in adult specimens running out in numerous, unequal, Bigmoidal 

 striae near the mouth ; the place where ribs bend backward is 



marked with a slight depression ; keel sharp, bounded on each 

 side by a furrow. 



This species is closely related to the preceding one from 

 which it is distinguished by a greater number of ribs. In a 

 specimen (fig. 2) which measures 63 mm. in diameter, their 

 number is about 53, while in one with the diameter of 48 mm. 

 there are about 55 of them in the last whorl. Fig. 1 shows 

 the largest specimen, 90 mm. in diameter and with ribs near the 

 mouth splitting into many finer ones. The proportion of the 

 shell-diameter to the umbilical width is about 10 to 4. 



Locility : — Nishi-Nakayama and Ishimachi ; quite frequent. 



3. HILDOCERAS INOUYEI M. 



PI. II. Figs. 5, 6. 



The shell is discoidal, much compressed, keeled, with a 

 narrow umbilicus, its breadth being about I or a little less of 

 the shell-diameter. Involution about I. The whorls are Hat with 

 obtuse sigmoidal ribs whose number varies between 4<> and GO 

 according to age. The umbilical wall is perpendicular, with its 

 edge rounded. Keel high and sharp, and bounded by a channel 

 on each side. 



This species resembles the two preceding in the shape and 

 surface markings of the shell, but is decidedly more narrowly 

 umbi Heated. 



