BELEMNITES OF THE OXFORD CLAY. 



115 



Few Belcmnitcs appear to have had so large a distribution in time and space as the 

 group allied to B. sulcaius of Miller and B. canalicidalus of Schlotheini. From the base 

 of the Inferior Oolite to the middle of the Oxford Clay they are generally recognised in 

 Europe ; specimens much like our examples from Oxford Clay are abundant in the country 

 south of Moscow ; others come to us from the Himalaya^ from Cutcli^ South Africa^ 

 New Zealand,* and Queensland.^ 



Belemnites sulcatus, Miller. PI. XXIX, XXX; figs. 71 — 75. 



Boference. Belemnites sulcatus. Miller, ' Geol. Trans.,' 2nd series, vol. ii, p. 59, pi. viii, 

 fig. 5 [excl. fig. 3 and 4]. 1823. 

 Belemnites Beaumontiamis, D'Orb., 'Pal. Fran^., Terr. Jur.,' p. 118, 

 pi. xvi, fig. 7, 11 (on the plate it is called B, Altdorfensis). 1842. 



Guard. Subcylindrical or conical in the alveolar region, more or less depressed in 

 the post-alveolar region and deeply grooved ; the groove interrupted or expanded toward the 

 apex, and gradually ceasing about the alveolar summit. Outline nearly straight on the 

 ventral, more curved on the dorsal aspect ; apicial region tapering, surface smooth or 

 granulated. Sections show the axis to be nearest the ventral face, very excentric, and 

 somewhat recurved. Near the apex the sections are almost circular or a little oblong. 



Greatest length observed 5*5 inches ; and of this the axis occupied 3 inches. Gre.'itest 

 diameter in this specimen 0"85, in a stouter specimen 1'05. 



Young. The very young form was more or less hastate (fig. 73 v^). Somewhat 

 advanced in age is the very rarely seen form fig. 73 y, from near Oxford; next we have 

 fig. 72 and 71 u, differing from full-grown specimens only in greater slenderness. 



Proportions. The normal diameter (not counting the groove) being taken at 100, 

 the transverse diameter of the alveolar apex is, in full grown individuals, 108 ; the axis 

 under 300 ; the ventral radius 40 ; the dorsal GO. In young specimens the axis is 500. 



PiiRAG.MOcoNE. Slightly arched, very obliquely inserted ; septa nearly circular, un- 

 usually approximate, their depth being about one eighth or even only one ninth of the 

 diameter in the anterior part; sphericle distinct and rather large; angle 22°. The 

 concave surface, within the septal edge, is a portion of a sphere, measuring 90° across. 



Observations. There is some variety in the sections of the guard ; some specimens 

 showing more depression than others ; in some the groove is broader, in others it is deeper ; 

 in a few the groove expands a little toward the apex (fig. 74 v), and also expands on the 

 surface over the alveolus (fig. 75 y') ; in some there are one or two lines parallel to the edges 



' Specimen in my possession. - Sowcrby, ' Geol. Trans.,' 2udSer., vol. v, p. 329. 



* Tate, in 'Geol. Soc. Journal,' 186", p. 151. * Hocbstetter, Novara-E.vpedition. 

 ^ Specimens in the Collection of Mr. Charles ]Moore. 



