1876.] 399 [Hyatt. 



Stephanoceras Sauzei. 



Amm. Sauzei D'Orb., Terr. Jurass., pi. 139. 



The thick tumid aspect of the young of this shell has caused me 

 repeatedly to place it in the same series with Gervilii, but a renewed 

 inspection has just as often brought me back to the same conclusion 

 that this was due entirely to the purely coronatum-like form of the 

 young, which at a very early stage is not round and smooth as in 

 Gervilii, but more like subcoronatum or Blagdeni. This remarkable 

 difference in the development confirms the contrast of structure 

 between the mouth of the shell with its ear-like lappets, and the plain 

 Humphriesianus-like outline of that of Gervilii. The form also differs 

 somewhat. The living chamber near the mouth becomes depressed 

 from above, as in Braikenridgii, instead of contracting laterally, as in 

 Gervilii, and all allied forms. There are several varieties, but the 

 principal are those with open umbilici, in which the young retain the 

 true coronatum form until a late stage of growth. These always seem 

 to have prominent tubercles at an early age, and are altogether more 

 similar to Braikenridgii than those with narrower umbilici. The last 

 are more involute, have the tubercles later developed, the ribs finer, 

 and the young in form and markings so similar to the young and 

 adults of Gervilii or Brongniartii that they are often confounded. 



This is one of the few instances in which the history of the devel- 

 opment and adult characteristics appears to be at variance with the 

 geological record. Braikenridgii has only been found in the Hum- 

 phriesianus-bed, whereas Sauzei is habitually found in the lower 

 part of the Humphriesianus-bed, the " Sowerbyii-bed." This, how- 

 ever, is only a slight discrepancy which may arise from false identifi- 

 cations, and I have therefore ventured to disregard it in the genea- 

 logical table. 



DOUBTFUL SERIES. 



Stephanoceras refractum. 



Naut. refractus Rein., Naut. et Argo, figs. 27-30. 



Amm. refractus D'Orb., Terr. Jurass., pi. 173. 

 " " Quenst., Der Jura., p. 524, pi. 69. 



This bent and distorted form has young which can be compared 

 only with the young of this series, and it is possible that a suffi- 

 cient number of specimens would enable an observer to trace it 

 directly to some one form. There is, perhaps, more resemblance to 



