346 Br. H. Woodward — On A^itychus and Apfi/c/wpsis, — 



specimen, in which the Aptychus is seen fitting the aperture of the 

 mouth of the shell (as first observed in Ammonites 

 suhradiatiLs from the Inferior Oolite of Dundry, and 

 described by the late Dr. S. P. Woodward, F.G.S. ; 

 see " Geologist," 1860, vol. iii. p. 328, and woodcut 

 figure), it will be necessary to re-examine with 

 great care all those forms of supposed Phyllopod- 

 shields which occur in beds in which Gonatities have 

 been found. But, even after this task has been 

 carefully performed, we feel convinced, with Herr 

 AmTnomte, with Dames : — 



FSfSi'^InT (^-^ ""^^^^ ^°^ °*^^''^' *^^^ explanation is, ac- 



Oolite Dundry. cording to our present knowledge, inadmissible." 



And here it is only necessary to refer the reader 

 to the Eeports drawn up by Professor T. Eupert Jones, F.R.S., and 

 myself,^ on the Phyllopoda, in order to confirm Herr Dames' own 

 conclusion that all the simple disc-like or bivalved-shields, met 

 with in the older rocks, cannot be referred to the opercula of the 

 Cephalopoda. 



Then as to the substance of these Apfychns-like forms, it is not 

 without interest to notice, that whereas the greater number of the 

 Mesozoic AmmonitidcB had thick shelly opercula, only a very few 

 had thin horny ones. I do not understand Herr Dames clearly if 

 he says that the Aptychi of Secondary Ammonites consist of only one 

 piece. I have examined a very great number, and they all have 

 a mesial suture and most of them readily divide into the two halves, 

 corresponding with the two conjoined dorsal arms, which form the 

 hood in the recent Nautilus, and which secreted the shelly operculum 

 in the Ammonites. 



There are many special characters about these Palaeozoic Phyllopod- 

 shields that, even when they are not found associated with body- 

 segments, will require to be carefully examined before they can all 

 be referred to Goniatites. 



We would draw attention to the varied form of the notch ; the 

 absence in some, and the presence in others, of the dorsal suture ; 

 the presence in different genera of the rostral portion of the shield 

 in the circular and oval forms, and the possible existence in some of 

 a hinder trigonal shield-piece {PJioladocaris, Dipterocaris) ; the shape 

 of the shield itself; the ornamentation; and, lastly, the substance 

 composing it. Usually it is possible to discern the difference in 

 character between Crustacean and MoUuscan structures, as also 

 between these and obscure ichthyic fragments. 



It is desirable to add, that many of the genera to which Herr 

 Dames takes exception were not hastily established, nor without 

 study on the part of their founders. Barrande and Salter always pro- 

 ceeded with extreme caution, and, if we have been sometimes misled 



1 Geol. Mag. 1883, Decade II. Vol. X. pp. 461-464. Op. cit. 1884, Decade 

 III. Vol. I. pp. 348-356, and more fully in lirit. Assoc. Eeports, Southport, 1883, 

 and Montreal, 1884, Section C. Geology. 



