28 FOSSIL MOLLUSCA OF THE CHALK. 



10. Ammonites Griffithii, Sharpe. Plate XI, fig. 3. 



A. testa discoided IcBvi^ sulcis 4 vel 5 Jlexuosis ornatd : dorso rotundato {impresso ?), 

 umbilico parvo : aperturd semiovali : semptorum marginibus ramosisshnis, lobis trifidis. 



Shell discoidal, smooth ; each whorl crossed by four or five slightly waved, transverse 

 furrows, bounded on each side by a slight elevation ; back rounded and marked in the 

 cast by a small medial groove; umbilicus small and well defined; whorls four fifths 

 concealed ; aperture semi-oval ; margins of the septa very complex, with four trifid 

 lateral lobes. 



Diameter, 5 inches ; width 2^ inches. 



Found in the hard Chalk of Aughanloe and Benbraddagh, in the County of Derry, by 

 the Ordnance Geological Surveyors. 



The specimens examined being all internal casts, the above description is necessarily 

 imperfect, and may require modification when better materials are found. The species is 

 nearly allied to A. Lewesiensis, Sow., and A. Mayorianus, d'Orb. ; it is distinguished from 

 the former by its transverse furrows, from the latter by less breadth at the back, and from 

 both by the want of transverse ribs, and a smaller umbilicus : the lobes of the septa of the 

 three species are much alike. The shell is named after Richard Griffith, Esq., to whose 

 labours we are indebted for the Geological Map of Ireland. 



11. Ammonites Austeni, Sharpe. Plate XII, fig. 1 and 2. 



A. testa discoided, compressd, transversim costatd ; costis Jlexuosis incequalibiis, 

 majoribus paucis ambulacrum amplectentibus, minoribus numerosis dorsalibus : dorso 

 rotundato : umbilico parvo : aperturd rotundato sagittatd. 



Shell discoidal, transversely ribbed : whorls flattened at the sides, rounded over the 

 back, ornamented with numerous unequal flexuous ribs, all passing over the back, of which 

 a few, larger than the rest, embrace the whole whorl, the others only reaching to the 

 middle of the side ; the number of larger ribs varies, being eight or ten on the whorl of a 

 young, and about twenty on that of an old shell : back narrow and rounded : umbilicus 

 small, and bounded by steep sides exposing half the inner whorl : aperture bluntly 

 sagittate. 



Diameter of the specimen fig. 1, 16 inches; height of outer whorl, 6 inches; width of 

 the aperture, 3^ inches : it often reaches much larger dimensions. 



Found in the Grey Chalk of Surrey, Kent, and Sussex, and in the Upper Green Sand 

 near Dorking. 



It is singular that a species to be found in abundance near London should never have 

 been pubUshed; it has probably been mistaken by collectors for A. jjlatiulatus, Sow., to 

 which it has some resemblance ; but that species has transverse furrows where this has 



