1918 AMMOMTES BIFROSS 114c 



The agreement is remarkable enough to suggest that this is Lister's 

 example and so is Holotype : at any rate it is a Topotype and worthy 

 to be Neotype. Mr. V. E. RoDSOR, F.G.S., purchased it in London. 



Genus, HilJoceras ; family Hildoceratidse. 



Geological position, Alum Shale, Whitby. 



Result 



Hi! h(.( ERAS BIFRONS, BRUGUIERE sp., ij.S.,, W'hitbian [subcarinatitm 

 [bijrons) zone], Whitby. 



Note 



In PI. CXIV b is depicted a cripple-form keel and furrows are lost, 

 periphery i> rounded and crossed by fairly strong ribs : Hyatt's planicostan 



abdomen. This example is slightly less umbilieate and thinner than 

 //. bijrons: the differences may be due to the injury which caused the 

 disturbance of venter ; but there is nothing to show; where the injury 

 took place. Return to a very early form of venter is to be noted as 

 result of injury local accelerated cyclical development. 



Comparable Species 



74 32 [27] 45 



F. 70, 36, [27?], 43, — Am. Walcotii, J. Sowcrby, Oct. 1815, evi, [1]. 



F. 68, 39, [25?], 35, — Am. Hildensis, Young & Bird, 1822, xn, 1. 



T. 200 25, 19, 49, I Mf fons; d'Orbigny, 1844, lvi, 



F. 200(95), 27, 19, 52, J J b J ' " 



T. I55(F. 160), 26, 19, 52,— Warpoceras bijrons; Wright, 1882, lix, 



1, 2. 

 F. 46, 39, 23, 32, l Hildoceras bijrons var., S. Buckman, 1889, 



j xxii, 30, 31, type of 



H. semipolitum, S. Buckman, 1902, p. 4. 



F. 56, 39, — , 31, I Hild. bijrons var. sulcosa, Bellini, 1900, 



( p. 146, f. 11. 



F. 57, 34, — , 44, — Hild. bijrons v. laticosta, Id., f. 12. 



F. 33, 37, — , 37, — Hild. bijrons v. serraticosta, Id., f. 13. 



And see No. 12 ; also Meneghini, 1867, Dumortier, 1874. 



