100 



[Senate 



GONIATITES OWENI (n.s.)- 



SflfiLL depressed suborbicular; umbilicus moderately large (varying in diflferent 

 individuals). Volutions five, six, or more; about one-sixth to one-fourth the 



. width of the volution showing in the umbilicus, three-fourths or more being 

 embraced in each succeeding volution. Aperture sublunate or semielliptical, with 

 the angles auriculate : sides of the volutions flattened towards the ventral 

 margin, and gradually curving to the dorsal side; the back regularly curved. 

 Surface (as preserved in the specimens examined) without markings. Dorsal 

 lobe elongate, a little wider above than below, and narrower in the middle; 

 extremity bifid : dorsal saddle highly arched, with a height equal to or greater 

 than its width at base; dorso-lateral lobe elongate, triangular, with a low 

 arching lateral saddle and a narrow triangular ventral lobe. • 



In the young state, and sometimes in older specimens, this species is marked 

 by transverse grooves or constrictions, extending around the outer volution and 

 giving a trinucleate aspect. 



This species is more rotund than the G, patersoni of the Hamilton group, and 

 the septa are less complex in their sinuosities. It is also more rotund and broader 

 on the dorsuc, with a larger umbilicus, than G. rotatorius, with which it is as- 

 sociated. 



The species appears to be variable in some of its characters, and we find two 

 somewhat constant varieties. The difference in proportional size of umbilicfts is 

 accompanied by other characteristics. In a specimen with a large umbilicus, the 

 dorsal lobe has the form described, and the extremity does not reach so low as 

 the arch of the saddle in the second septum behind; while in specimens with a 

 small umbilicus, the sides of the dorsal lobes are quite parallel, and the periphery 

 of the shell is marked by a pair of continuous grdoves parallel with the sides of 

 these lobes; and the extremities reach beyond the arch of the saddle in the second 

 septum behind. This feature indicates a closer arrangement of the septa through- 

 out, which does not appear to be due to age. 



For this variety I would propose the name of G, paralhla, from the lineal 

 grooves on the periphery bordering the dorsal lobes. 

 11 



GONIATITES OWENI. 



Fio. 11, View of a specimen with the larger umbilicus. 



Fia. 12. Septa of the same produced, in their natural relations. 



