448 MR. S. S. BUCKMAN ON THE 



Later on, there is considerable likeness to a j'-outhful Blagdeni; 

 and, while still very young, the distinctive zigzag-ornaments are 

 assumed. So far as the inner whorls are concerned, there is no 

 definite evidence against descent from Zurcheria, though descent 

 from Stephanoceras is quite as probable. It is only in the later 

 developments that the latter probability becomes almost a certainty. 

 These developments, which I shall have to describe, are so much 

 like the developments of the IStepTianocerata, and so unlike those of 

 Zurcheria and its allies (Amaltheidce), that I come to the conclusion 

 that zigzag is nothing more than a rather peculiarly ornamented 

 development of the petUis-Blagdeni stem.^ Its suture-line (see 

 PL Xiy. fig. 1) supports this view. 



Stephanoceeas zigzag and its Developments. 

 Series a. 



Roughly speaking, there are two principal forms called ^ zigzag'^ — 

 a thin and a thick one. I consider it advisable for the sake of 

 clearness to confine the specific name to the former. A specimen 

 (exhibited when this paper was read) which agrees with d' Orbigny's 

 fig. 9 may be considered as the type of the species. It is a little 

 larger than d'Orbigny's specimen, and shows the change in ribbing 

 not observable in the Prench fossil. A similar example, changing its 

 ribs at the same period, possesses the complete mouth-border — a well- 

 marked lateral spatulate ear, of which the outer portion had not, 

 apparently, been properly calcified. 



A most important specimen, illustrating the law of earlier inherit- 

 ance, shows a change of ribbing beginning nearly a whorl earlier 

 than in the first mentioned, and, in fact, this specimen is not a true 

 zigzag, but a marked development thereof. (It should be noticed, in 

 view of some remarks later on, that, on the core, there is a distinct 

 interruption of the ribs in the middle of the ventral area.) In the 

 specimen depicted (PI. XIII. figs. 1, 2) a still further development 

 in the same direction is to be noted. In this example nothing but 

 the early whorls of the centre show the zigzag style of ribbing — 

 all the rest of the specimen has what might very appropriately be 

 called annulose and bifurcate-annulose ribbing,^ with small knobs 

 at the point of bifurcation. 



This form is very near to Seebach's procerus,"^ and possesses the 

 same kind of ribbing.^ But Seebach's fossil is just the next step 

 onwards, which has begun to acquire what may be called two- 

 new characters — increased inclusion and broader, more inflated 



^ See Monogr. Palaeontogr. See. Part vi. p. 271. 



- The claims of the word zigzag to a classical origin appear very doubtful, 

 but it may be admitted on account of long usage. 



3 A single rib encircles the whorl or bifurcates at the edge of the lateral area. 

 The alternation of the two styles of ribbing is not quite regular. 



* Seebach, ' Der Hannoversche Jura,' pi. x. fig. 2 a, c. 



^ Ibid. p. 1 55. 



