AMMONITES. 51 



are not opposite to one another, but alternate : ribs flexuous, rising in threes from twelve 

 large tubercles which surround the umbilicus, forming an irregular zigzag pattern on the 

 side of the whorl, and ending at twenty-four rather smaller tubercles on the side of the 

 back : two rows of tubercles on each side of the shell : umbilicus small, allowing about 

 one third of the inner whorls to be seen : aperture oblong : septa with the dorsal lobe 

 considerably longer than the trifid superior lateral lobe. 



Found by Mr. Wiest, in the Chalk with silicious grains, at Chardstock, Somersetshire. 



42. Ammonites Ramsayanus, iS/iarpe. Plate XXIII, fig. 4a — c. 



A. testa discoided, costatd, tuberculatd : anfractibus paucis, sub-compressis ; costis 

 continuis, bi-tuberculatis, ad dorsum bifurcantibus : dorso laio, rotundato, costato, utrinque 

 tuberculato : umbilico parvo : aperturd oblongd. 



Shell discoidal, with few, slightly flattened whorls, and a broad, rounded back : the 

 whorls are ornamented on the sides by twenty ribs, each of which rise from a small tubercle 

 at the edge of the umbilicus, and bear another larger tubercle near the back ; at the latter 

 tubercle each rib divides into two smaller ribs, which continue across the back, and unite 

 again at the corresponding tubercle on the other side of the back : umbilicus small, 

 allowing nearly half of the inner whorls to be seen : aperture oblong : the septa have not 

 been seen. 



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



Very rare in the Chalk with silicious grains, at Chardstock, Somersetshire. 



The only specimen which has been seen of this species is deformed, owing, without 

 doubt, to an accident met with when very young. In consequence of this malformation, 

 the two sides have very little resemblance to each other ; and the specific character given 

 above may prove incorrect when more perfect specimens are met with. 



A. Mamsayanus belongs to the group of the Coronarii, which, for the most part, belong 

 to the lower and middle divisions of the Oolitic series : its nearest congeners are perhaps 

 A. Humphriesianus and A. Brackenridgii. It is the second species of that group which 

 has been found in the Chalk ; A. catinus having been the first. 



This species is named after Professor Ramsay, of the Geological Survey of Great 

 Britain. 



43. Ammonites Feraudianus, D'Orb. Plate XXIII, fig. 6a — c. 



[" A. testa compressd, transversim costatd : costis incequalibus, rectis ; dorso complanato, 



