26 



one. In this instjince each spine arises from the inner margin of the 

 smaller whorl ; they are at first ])ressed a little downwards, and then 

 curve upwards so as to rest against the nml)ilical wall, though they 

 scarcely reach to its maigin above. One of the spines is fully half an 

 inch in length; it is ilattened and rather obtusel}' pointed. The com- 

 pression of the spines and their peculiar curvature are obviously the 

 result of abnormal compression or distortion. Traces of spines were 

 afterwards observed in other specimens, but all the additional informa- 

 tion afforded is that they sometimes proceed from the outer as well as 

 the inner parts of the sides, that they are occasionally acuminate, with 

 a dilated base and slender point, also that they are often covered up bj^ 

 the whorls as the shell increases in age. In every place where they 

 were traced, they Avere found to be protected from injury by the support 

 afforded by the inner margin of the whorl next to the one on which, they 

 were placed. 



Most of the tubercles become obsolete or disappear on the body whorl, 

 excepting oidy a row of large ones round each umbilical margin, and 

 another of much smaller size, placed about the middle of the sides. 

 The ribs on this volution are alternatel}^ bifurcating and simple, but they 

 are all of equal length, and bear iisually a similar, or rather corres- 

 ponding number of tubercles. The row of large tubercles round the 

 umbilical margin gives to that opening a distinctly coronated aspect, 

 but those on the middle of the sides are sometimes so small as to be 

 barely perceptible. The aperture of the original of fig. 1, on Plate IV., 

 is about three inches and three-fourths wide, b}' three inches and one 

 line in height. 



Seven specimens of this "strongly characterized" species were 

 obtained, most of which are curiously distorted. ISTone of them are very 

 perfect, and yet nearly all of the essential peculiarities of the fossil are 

 well exhibited in one or the other, except the outlines of the septa and 

 the shape of the outer lip. 



In the preliminary report previously referred to, Mj-. Billings says 

 that the specimens Just described are nearly related to Ainmonites Stolics- 

 A-anus, but that they are "perfectly distinct" from it. The difference 

 between the shells from the two localities seems to the writer to be scarcely 

 of specific importance. A. Stoliczkanus was originally described from a 

 single half grown example, about three inches and three quarters in dia- 

 meter. Apart from the circ umstanee that some of the tubercles originally 

 bore long S])ines, (a feature seen so rarely even now that there is no 

 wonder that it was not observed before) Mr. Gabb's description of the 



