22 AET. 2. — H. YABE : CRETACEOUS 



suturai by which fact it is distinguished from Helicoceras. On 

 the portion of the irregular growth, however, the siphuncle i& 

 always (?) situated in the median line of the external side. 



The suture line was partly examined on the whorl which 

 succeeds the regular spiral growth. It shows two saddles and 

 corresponding lobes on one side of the siphonal line, and does 

 not essentially differ from that of H. Otsukal. The two saddles 

 are comparatively slender and nearly equal in height ; both are 

 bipartite with bifid subdivisions. The lateral lobe is very broad 

 and bipartite, slightly exceeding the ventral one in depth. The 

 siphonal saddle is relatively broad and high, with a few ser- 

 rations along the margin. 



The complicated mode of coiling the whorls in this species 

 is better seen in the accompanying figures. In Plate IV., figs. 

 4 and 5 show its external aspect seen from two different direc- 

 tions, each U-shaped curve is marked with the Koman numerals 

 II. — VI. and I'. II'. in the order of their succession. The 

 first carve (I.), immediately succeeding the spiral portion, is not 

 to be seen in these figures ; the second curve which is only 

 partly visible is marked II. and the third III. and so on. The 

 seventh curve, being nearly upon the first one, is marked I'. 

 and the eighth, for the same reason, II'. 



Fig. 6 shows a longitudinal section of the specimen, the 

 cross-sections of the whorls being hatched. The two volutions 

 of the spiral portion appear as four round sections marked with 

 Arabian numerals 1-4. The position of the siphuncle is also 

 indicated on the sections by S. 



Fig. 7 was drawn after a wire model showing the mode of 

 coiling the whorls from the beginning to the end. Roman 

 numerals are here also used in the same sense as before. 



