AMMONITES. 45 



34. Ammonites Saxbii, Sharpe. Plate XX, fig. 3. 



A. testa discoided, compressd^ tuberculato-costatd : anfractibus panels, complanatis, an- 

 gulatis' dorso piano, hi-tuhereulato -, costis reetis 8 — 10 majoribus tri-tubereulatis, 20 mi- 

 noribus bi-tuberculatis • aperturd rhomboided •' septorum lobis later alibus bijidis. 



Shell discoidal, compressed ; whorls few, flattened on the sides : back flat, with angular 

 edges, and a row of tubercles on each side : ribs about thirty, straight, of which eight or 

 ten rise from a tubercle on the edge of the umbilicus, and the others begin on the middle 

 of the side of the whorl ; all ending in a large tubercle at the side of the back, and also 

 bearing a smaller tubercle before reaching the back ; there being either two or three of the 

 smaller ribs between every two longer ones : apertm'e rhomboidal : umbilicus small, 

 bounded by steep sides, aod allowing two thirds of the inner whorls to be seen : lateral 

 lobes of the septa bifid. 



Diameter, 1 inch; height of the last whorl, ^ inch; width of the aperture, f inch. 



Rare in the Grey Chalk of Ventnor, Isle of Wight. 



A pretty little shell, readily distinguished from all the varieties of A. varians by its 

 straight ribs and want of keel. It is named after S. Saxby, jun., Esq., who has rendered 

 me much assistance in collecting together the fossil species of the Chalk of the Isle of 

 Wight. 



35. Ammonites Vectensis, Sharpe. Plate XX, fig. 4. 



A. testa discoided: anfractibus, lateribus compressis, dorso rotimdatis, transversini 

 costatis: costis incequalibus, jlexuosis, supra dorsum continuis: wnbilico mediocri ; aperturd 

 ovali. 



Shell discoidal, with few whorls, which are flattened on the sides, rounded at the back, 

 and crossed by about twenty flexuous, slightly elevated ribs ; the ribs commence at the 

 edge of the umbilicus, and slope forward to the middle of the side of the whorl, where 

 they bend backwards a little way, and then again slope forwards over the back ; besides 

 these there are about ten shorter ribs occasionally inserted between the former, which only 

 begin on the middle of the side, and equally cross over the back : umbilicus of moderate 

 size, leaving more than half the inner whorls exposed : aperture oval : septa not seen. 



Diameter, 2^ inch ; height of last whorl, 1 inch ; width of aperture, f inch. 



Only one imperfect specimen has been seen, which was found in the Chloritic Marl, 

 near Ventnor, Isle of Wight. 



This species is related to A. consobrinus, D'Orbigny, and A. cinctus, Sowerby, but is not 

 in danger of being confounded with either. It is also related to A. undatus, Sowerby ; but 



8 



