304 ME. s. s. B TIC KM AN OX Lvol. Ixxiii, 



Another example, about same size and matrix, and a smaller 

 specimen with matrix decomposed to light Yellow, presented by the 

 late E. Wilson, F.Gr.S. Another example, matrix soft, decomposed 

 to light blue (purchased) : all from the same place. And see note 

 to next species. 



MiCEODEROCEEAS SEPTI&EEEM, nom. nOY. (PI. XXX, figS. 2« 



1844. Ammonites lircliii J. Bucknian pars {non J. Sowerby), ' Geologj' of 

 Cheltenham' new ed. p. 88. 



Description. — Serpenticone ; plat^'-perpachygyral, perlatum- 

 bilicate to pachygyral latumbilicate ; bituberculate ; septitubercu- 

 late ; periphery tiatly rounded, subarci-costulate. 



Remarks. — This is an inflated deYelopment of Ammoiufes hirclii 

 by way of the last species {21. depressuni), but it has not attained 

 to the inflated proportions of the next species (J£ injiatuni). 

 though it has passed that species in the differentiation of the outer 

 tubercles compared to the inner — the character seen at a later date 

 in Deroceras {D. bispinic/erKin, p. 302) and later still carried to 

 unituberculation . 



This species is best understood by comparison with M. injlatum. 

 Its thickness is some 7 per cent, less at 64 mm. diameter, and the 

 periphery is somewhat flatter. The ornament is similar, but the 

 spinicostse are about 50 per cent, wider apart, and the outer row 

 of spines is shown by the septate areas to be more dcYcloped and 

 more differentiated from the inner. The conspicuous septate areas 

 which are somewhat B-shaped suggest the trivial name : the outer 

 (top) loop is broadly, and the inner narrowh-^, elongate with a thin 

 connecting area — thus the partition extended not only under the 

 spines, but also under the connecting rib. 



Proportions are tabulated beloAv (p. 306). 



History of the figured specimen. — The original label, 

 skeleton printed, on the specimen reads : ' X'ame A. Birchii, 

 Loc. Lias, Cheltenliam, Col. by J. JBiicliinan,' — the words in italics 

 flUed in in his handwriting. The matrix is light blue with crinoid- 

 stems, small gastropods, small lamellibranchs, and broken organisms. 

 See below% p. 312. 



[Note. — Since this paper was written I find that I have over- 

 looked another of my father's specimens of Ammonites hirchii 

 ( S. B. coll. No. 2115). It has a quite different matrix — blue and 

 pyritic ; but bears the same label, which thus may mean ' close to 

 Cheltenham' rather than ' Cheltenham district' : see belovr, p. 312. 

 Its proportions are S. 72, 28, 29 (31), 49 ; S. 114, 26, 28 (29), 51. 

 Spines are approximate and somewhat small — 38 on last roAV of 

 outer whorl. It is an example of Microderoceras depressum, see 

 above. On one side is an impression of a portion of another 

 21icroderoceras, of about the same size, showing obsolescence of 

 spines, of interest in connexion with remarks below, p. 307.] 



