METOICOCERATID. 121 
The sutures in the two specimens here described as swallovi are some- 
what abraded, but their details of outline are sufficiently well preserved in 
different sutures to enable one to see how much simpler they are than in 
M. whitei. his simplicity of the marginals is not so great in some speci- 
mens as it is in fig. 2 of Pl. XIII, since in the suture (Pl. XIII, fig. 1) the 
second lateral is trifid and in fig. 13 the fourth lateral saddle is bifid. The 
number of inflections on the sides appears to ‘be less in this species than in 
whitei, five only being present on both sides, with saddles at the lines of 
involution; and in the fossil shown in Pl. XI, fig. 16, there is the same 
number, with a lobe at the line of involution. 
Locality: Grayson County, Tex.; Utah. 
Age: Colorado epoch. 
@ 
METOICOCERAS GIBBOSUM n. sp. Hyatt. 
Pl. XV, figs. 5-8. 
The single fossil upon which this species is founded could not be 
placed in any of the species here described under the same genus. It 
has stouter, broader volutions than any of these, and, instead of becoming 
more compressed as it grows older, continues the same rate of increase 
in the transverse diameters The involution is about the same as in 
M. swallovi, but there are no nodes on the umbilical shoulders at any stage, 
although the alternating longer coste reach to the umbilical shoulders. 
Their greatest prominence is at a short distance ventrad of the 
umbilical shoulder. The costations are like those of the oldest stage of 
whitei, i. e., regularly long, prominent costze alternating with short ones. 
The two outer lines of tubercles do not differ from those of other 
species. The sutures are intermediate between the simpler character 
of those of M. swallovi and the more complex outlines of those 
of M. whitei. The first lateral saddles and lobes have about the 
same general aspect as those of M whitei, but the auxiliaries are 
similar to those of M. swaillovi, except that the second lateral saddle shows 
small marginals and a tendency to division on its outer side, which has not 
been observed elsewhere. The third lateral saddle shows in some sutures 
of the left side a tendency to become divided, which is necessarily 
exaggerated in the drawing and which is entirely absent in many sutures, 
