1874.] 23 [Hyatt. 



iEgoceras Boucaultianum Hyatt. 



Amm. Boucaultianus D'Orb., Terr. Jurass., Ceph., p. 294, pi. 90. 



This remarkable species differs from Leigneletii in about the same 

 manner that that species differs from JEgoceras Charmassei, in other 

 words, it is more involute than Leigneletii at the same age ; on about 

 the seventh or eighth whorl, at least three-fourths of the sides are 

 hidden. The pilae are not so coarse as in that species, and the ab- 

 dominal channel is obliterated at an earlier age, and succeeded by 

 the crenulations caused by the pilae. The septa differ considerably 

 The specimen examined was one of D'Orbigny's types. The same 

 transitional forms which lead into Leigneletii also lead into other 

 more compressed and more involute forms which are transitional to 

 the true Boucaultianus. They differ from Leigneletii only in the 

 suppression of the tuberculated pilse, and a general tendency toward 

 obsolescence of the pilae on the sides. 



Appendix to Communications on Reversions among 

 Ammonites. 



Proc, Vol. xiv, 1870, p. 22. 



Microderoceras Birchii. 



This occurs in the form named Amm. rotundaries by Fraas (mss.) 

 in the Arietenbank or Bucklandibed. 



Microderoceras Hebertii. 



This is not the Hebertii of Oppel,but a form intermediate between 

 that figured by D'Orbigny under the name of Amm. brevispina and 

 the typical Birchii. It is not found in the Middle, but in the Lower 

 Lias Birchiibed at Semur. The confusion arises out of a false iden- 

 tification by Oppel from the supposed types in D'Orbigny's collection. 

 The type is really a very rare form of Birchii, found only, so far as I 

 know, in the Museums at Semur and Cambridge. The specimens in 

 D'Orbigny's collection are forms of the single-spined group allied to 

 armatus. They differ from the type described by D'Orbigny, and 

 also from Hebertii of Oppel, which is identified in Germany, and 

 appears in the Munich collection as a species allied to Valdani, with 

 a keel, and all the characteristics of its group. 



Microceras biferum. 



The young of this species in some varieties is very similar to the 

 y oung of Birchii, and confirms • the views previously taken of their 

 affinities. 



