254 G. C. Crick — Note on Ammonites euomphalus, Sharpe. 



shell passes from a diameter of 21-omm. — the diameter of the 

 type-specimen — to its greatest diameter, viz. 43 mm., in about three- 

 fourths of a whorl. The first fourth of this portion is wanting. The 

 last half-whorl is well preserved ; on its lateral area the smaller ribs 

 completely disappear, while the spines on the larger ribs become 

 relatively larger, the inner one only slightly, but the outer one 

 considerably. The pairs of strong ribs on the periphery connecting 

 the large lateral spines are well developed. Of the tubercles on the 

 anterior rib of each pair, that on each side of the median line of 

 the periphery becomes with age relatively much smaller, while 

 the corresponding tubercle on the posterior rib becomes much larger, 

 the rib itself becoming at the same time much less distinct ; the rib 

 at the anterior lateral spine that is preserved is very feeble. The 

 intermediate ribs almost entirely disappear at the anterior part of 

 the specimen ; the tubercles on the rib which is situated about 

 half-way between two lateral spines gradually increase in size, 

 especially the one on each side of the median line, that on the 

 median line being well marked, but smaller and more obtuse than 

 the others. With considerable difficulty the suture-line has been 

 traced on this portion of the fossil, namely, at the point marked 

 s in Figs. 2a, h, where the diameter of the shell is about 34 mm. ; 

 it is represented in Fig. 2c. 



Although this specimen considerably increases our knowledge of 

 Sharpe's species, we are not yet in a position to give the characters 

 of an adult shell. 



As will be seen from a comparison of Figs. 1 and 2, there are 

 certain differences between the originals of the two figures. A very 

 obvious difference is in the number and size of the lateral spines. 

 The example represented in Fig. 2 has fewer and relatively stronger 

 spines than the original of Fig. 1 ; the former has only five large 

 lateral spines in the last half of the outer whorl, whereas the latter 

 has twelve large spines in the outer whorl, seven of these being in 

 the last half- whorl. Unfortunately the inner whorls of the example 

 represented in Fig. 1 are not well preserved, but their ornaments 

 seem to agree very closely with those of the type-specimen, the 

 :spines on the inner whorls of the original of Fig. 2 being relatively 

 further apart. There are also differences between the suture-lines 

 of the two specimens ; some of these may be due to the spiny 

 •character of the shell, the suture-line varying somewhat according to 

 the position of the septum with regard to the spines. The specimens 

 were, however, found at the same locality and on the same horizon ; 

 hence, notwithstanding the differences just mentioned, we are 

 inclined, in the absence of more satisfactory material, to refer these 

 examples to the same species, the example depicted in Fig. 1 being 

 probably more like the adult of Sharpe's type than the original of 

 Fig. 2. 



In regard to the affinities of this species, Sharpe correctly pointed 

 out that it was allied to Ammonites Martinii, D'Orbigny,^ a species 



1 A. d'Orbigny : Pal. Frau9. Terr. Cret., vol. i (1841), p. 194, pi. Iviii, figs. 7-10. 



