12 MOLLUSCA FROM THE GREAT OOLITE. 



Ammonites arbustigerus, D'Orb. Plate II, figs. 4, 4a. 



Ammonites arbustigerus, D'Orb. 1848. Pal. Fran?., Terr. Jur., p. 414, t. 143. 



— — If Orb. 1850. Prod. Paleont., p. 296. 



A. Testa compressd, anfractibus rotundatis, latis, lateribus convexis transversim 22 

 costatis ; costis obtusis bi-trifurcatis vel intermediis, dorso sub-convexo ; aperturd oblongd, 

 compressd. 



A discoidal, costated shell, with somewhat convex and gradually increasing volutions ; 

 umbilicus large : the principal costse are obtusely rounded, and about twenty-two in number, 

 bifurcating as they pass over the back, having occasionally an intermediate rib ; back 

 convex ; aperture oblong. 



Locality. In the Great Oolite of Minchinhampton, and described by M. D'Orbigny 

 as occurring both in the Great and Inferior Oolite of Normandy. 



Ammonites macrocephalus, Schloth., var. Plate II, figs. 3, 3 a. 



Ammonites macrocephalus, Schloth. 1813. Min. Tasch. vii, p. 70. 



— — Schloth. 1820. Petref., p. 70, No. 16. 



— — Zieten. 1830. Pet. Wurtemberg, t. 5, f. 1, 4. 



— — D'Orbigny. 1848. Pal. Franc. Terr. Jur., p. 430, t. 151. 



— — D'Orbigny. 1850. Prod. Paleont., p. 127. 



A. Testa discoided, sub-ylobosd, anfractibus involutis, rotundatis, costatis: costis 

 20 — 30 obtusis, medio laterum bifurcatis; aperturd semi-ellipticd ; umbilico subcontracto. 



An inflated, or somewhat globose shell, with rather depressed volutions, and a narrow 

 and deep umbilicus, from the margin of which arise about twenty to thirty obtuse ribs, 

 which bifurcate in passing over the back. Back convex ; aperture semi-elliptical. 



We have ventured to assign our specimens to the Ammonites macrocephalus of 

 Schlotheim, although their imperfect state of preservation renders this identification 

 somewhat doubtful. The specimens of this species hitherto obtained by us from the 

 Oolite, are always in the state of casts, and very much eroded, so that the principal ribs 

 which surround the umbilical cavity, are nearly obliterated, as shown in the figure, 

 tab. 2, fig. 3. 



Locality. Great Oolite near Minchinhampton. 



Ammonites gracilis, Buckman. Plate I, figs. 3, 3a. 



Ammonites gracilis, Buckman. 1845. Geol. of Chelt., p. 104, t. 3, fig. 6. 



A. Testa discoided, compressd, anfractibus ovatis lateribus sub-complanatis, transversim, 

 30—40 costatis ; costis bi-trifurcatis vel intermediis, in dorsum continuis, aperturd ovatd, 

 sub-sayiltatd. 



A discoidal, compressed, ribbed Ammonite, with six to eight oval, slowly increasing 



