450 Foisils of the Chazy Limestone. 



be projected through the outer angles of these two species, it will 

 be seen that in one the animal must have lived nearly altogether 

 below this plane, and in the other nearly altogether above it.. 

 There are numerous species with about half the bulk of the 

 shell above and half below, and others with every intermediate 

 proportion. 



Notwithstanding the great number of species in this genus, all 

 attempts at a subdivision have hitherto failed. A number of 

 small groups of species having some peculiarity in common might 

 be pointed out, but these would not differ from each other gene- 

 rically r For convenience in classification, De Koninck makes 

 two large groups. 



1. — The Ornate, with angular whorls and the surface richly 

 ornamented with ridges and tubercles. 



2. The Globose, of which the form is more or less globular, 

 and the surface not at all or only moderately ornamented. 



This last group is divided by D'Orbigny into the Perspec- 

 tive, with the umbilicus so wide that all the whorls can be seen 

 in it, and the Falcate, with the umbilicus very small or alto- 

 gether closed.* 



Scalites is not a genus, but rather a small group of species dis- 

 tinguished by having the outer edge of the whorls angular, the 

 upper surface sometimes flat and at right angles to the longitu- 

 dinal axis of the shell, the spire sometimes elevated and consist- 

 ing as it were of a series of rectangular steps and the umbilicus 

 sometimes closed. The extreme form of the group is S. angu- 

 latus, which, by its. elevated spire, indicates an approach to the 

 genus Murchisonia. 



The genus Raphistoma was originally founded upon three 

 species of Scalites, and appears to have been designed to take 

 the place of that genus, for we find that, in his generic descrip- 

 tion, Professor Hall has the following remark : '* It is probable 

 also that the generic characters here given may be so extended 

 as to include the Scalites figured above, as I have some evidence 

 of the existence of the characteristic markings upon that shell." 

 PalaBont. N. Y., Vol. I., p. 28. The following are the views of other 

 authors upon the affinities of Scalites, so far as I can ascertain. 



* See L. De Koninck, Description des Animaux Fossiles qui se trou- 

 vent dans le terrain carbonifere de Belgique, Vol. I. p. 364. Also 

 Alcidb D'Orbigny, Paleontologie Franchise, Terrains Cretans, Vol # 

 II. p. 239. 



