-1 I OND, OR SCHLOTHEIM1 \N BK VN< II I ,| 



their old proportions. In the full adult condition the characteristics <>f the 

 sutures differ considerably from those of the typical Arietidas, and approximate 

 to 1 



The seventh whorl increases in >:/<■ with great rapidity, the abdomen be- 

 coming narrower, r i i « * channel shallower, the pilaa more depressed, losing their 

 prominent somewhat abrupt genicular bend, and on the abdomen becoming 

 depressed t<> a level with the uphonal line. The involution of this whorl is 

 about two fifths, and that <>f the ninth a trifle over one half. The peculiar flatten- 

 : the sides :m<l form "I" the adult whorl, and the amount of involution, are 

 approximations t<> the adult characteristics <>f Amm. (I^i but the 



lifferent and tin 1 young more robust; the pilaa are developed earlier 

 and more rapidly, and the abdominal channel also. In some specimens, however, 

 last are n>>t noticeable until unite a late period, the pilsB being continuous 

 - the abdomen, as in Der pianicostum, even <>n the sixth volution. 

 In the collections at the Stuttgardt Museum are several very fine specimens 

 of the old age of this species, and it is easy to distinguish it from Charmassei by 

 the narrowness of the whorls and its more open umbilicus and discoidal aspect 

 <»ii'- of the largest of these measures 195mm., the last whorl 17 mm.; another 

 315 mm., and the last whorl 18.5 nun. 

 In the Museum at Stuttgardt, in the centre of a crushed specimen of the true 

 angutata from Kirchheim, the young was very clearly exposed. This had very 

 :i and round, though rather stout whorls. The pilae appeared <>n the Bides 

 it folds, which are straight at first, then curve, reach the abdomen, and 

 finally cross it with a forward inflection. These become very prominent and 

 decided before the channel is formed, which finally cuts through the pilae. This 

 on, however, is considerable, since in the adult <d' this specimen the channel 

 is only partially developed, the pilaa being only about half cut through, though 

 the specimen is about two and one fourth inches in diameter. There is here a 

 the trias forms, but not to the tru< which the 



emble closely. They resemble Waehneroceraa very closely. 

 i ■ii- uric- observed in young specimens in P Quenstedt's 



collection, and in tin- Museum of Comparative Zool< 



[< '-... that after the channel is developed, and the Bhell is 



quit»- large, the pilaa again cross the abdomen, but this is not so Frequent as 

 ha- been supposed. They oftener remain separate until old a 



The original ol I Sow., which we »w in the British Museum, is 



only a malfoi m< I 



