1876.] 397 [Hyatt. 



adult characteristics appear to indicate a close relationship also to 

 microstomum. find also in my notes that one specimen in D'Orbig- 

 ny's collection had young resembling Humph riesianum. The only 

 safe conclusion, therefore, is to provisionally trace it back to Brocchii 

 as a direct derivative. 



There is one significant fact not mentioned by D'Orbigny, which 

 his specimens show. The abdomen is furrowed in many specimens. 

 The mouths, also, of the originals are more compressed than in his 

 figures 2, 4, 8, pi. 141. There is one specimen of this species in 

 the collection at Munich having a most remarkable resemblance to 

 Amm. globosus in the form and also in the outlines of the mouth. 



TENTH SERIES. 



Stephanoceras Braikenridgii. 



Amm. Braikenridgii Sow., Min. Conch., pi. 184. 



Amm. contractus Sow (pars), Min. Conch., pi. 500. 



Amm. Braikenridgii D'Orb., Terr. Jurass., pi. 135. 



This species has given great trouble to all who have undertaken to 

 study the question of its affinity. Quenstedt long since pointed our 

 its close relationship to Humpliriesianus nodosus. The large ear-like 

 expansions, however, which it possesses at an early age, cast more or 

 less doubt upon this apparently unavoidable conclusion. The large 

 and quite complete suite of specimens in this Museum and at Bristol 

 leave, however, but slight room for doubt that Quenstedt was right. 



The young in nearly all cases are strictly similar to the young of 

 subcoronatum, however much the adults may vary in form and char- 

 acteristics; a small number of them, however, especially from Dun- 

 dry, England, are very similar to contractum from the same locality 

 though they upon close examination exhibit differences in the thinner 

 forms and slower increase of the shell by growth and in the coarser 

 ribs. 



Oppel identifies Brocchii with contractum, and this appears to be 

 true in most collections, but an examination of the young of such speci- 

 mens from Dundry shows at once that they in part are true Brocchii, 

 and part belong to this species. The contractum described and fig- 

 ured by Sowerby I have seen, but my notes thereupon are not sat- 

 isfactory. Whether any species is really intermediate between this 

 and the subcoronatum in all its characteristics I cannot say, but any 

 one who will consult the descriptions of Amm.fuscus by Quenstedt, 

 Der Jura, p. 475, which may or may not have the peculiar broad 



