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Surface marked by transverse, tuberculated ribs, which are usually simple 

 but occasionally bifurcate. One comparatively large and long rib usually 

 alternates with two smaller and shorter ribs, and each rib bears six 

 small, distant tubercles on each side of the siphuncle. Septum, much as 

 in Acanthoceras mamillare (Schlotheim). 



An unusually perfect but very small specimen collected by Dr. New- 

 combe, a little over an inch in its maximum diameter, the original of figs. 

 3 and 3 a on Plate 35, has four tubercles on each rib, on each side of the 

 siphuncle, arranged as follows : one small tubercle on the umbilical mar- 

 gin, one half-way across the side, and two tubercles close together, just 

 outside of the siphuncle. 



Fig. 14. Acanthoceras spiniferuvi. Outline of transverse section of a small specimen, 

 to show the relative position of the two sets of tubercles on each side. 



The following notes on the specific relations of A. spiniferum have 

 been kindly communicated by Dr. Franz Kossmat, of the University of 

 Vienna, to whom one of the medium-sized specimens collected by Dr. 

 Newcombe was sent in March, 1896, for comparison with A. laticlavium, 

 Sharpe, var. Indicum, Kossmat. 



'^Acanthoceras Stoliczkanum, var. spiniferum, Whiteaves. 



" I have been quite surprised by the close resemblance of this species 

 to our European Acanthoceras mamillare (Schlotheim), one of the most 

 common fossils of the European Gault (Albien), known also in the Creta- 

 ceous deposits on the western coast of Africa. The specimen you have 

 so kindly sent me is characterized by a very peculiar ornamentation, con- 

 sisting of two sets of tubercles on each side. 



" Each of these sets is composed of three tubercles, which are spirally 

 elongated and sharpened in set 1, and rounded in set 2. The two sets 

 of tubercles are separated from each other by a greater distance than the 

 interstices between the tubercles in either set. On A. mamillare also, 

 in middle stages of growth, there are two sets of tubercles on each side of 

 the siphuncle, which arise from two tubercles only (in youth stage) by 

 successive division, the same as you observed in A. spiniferum,. The in- 

 ner tubercles on the inner whorls are often somewhat spinous (Comp. P. 



