478 PALEONTOLOGY OF NEW YORK. 



elongate lateral saddle, the apex of which is almost precisely in the centre 

 of the lateral face of the volution, and much in advance of the summit of the 

 umbilical saddle ; on the outside of this is another lobe similar to the first, 

 and a peripheral saddle in which the summit is still more advanced than the 

 one on the umbilical margin, and less advanced than the central one. These 

 characters of the lateral face are better shown in figure 12 of plate 72 than in 

 the figures on plate 73. The suture-lines are strongly marked and usually 

 deeply impressed upon the weathered surfaces. Siphuncle minute ; not 

 satisfactorily determined. 



Test and surface-markings unknown. Upon the peripheral margins of 

 some of the casts there is an impression indicative of the imprint of curving 

 strite, which may mark the margins of the sinus. 



The internal casts are smooth, with the exception of the deep indentation 

 along the suture lines. The fossil usually occurs in a fragmentary condition, 

 and few entire individuals have been observed. These measure from sixty 

 to sixty-five mm. in their greatest diameter; but fragments of other indi- 

 viduals of larger size indicate that the shell has had a diameter of eighty or 

 ninety mm., exclusive of the chamber of habitation. The slender and much 

 expanded form has rendered it more easily broken and dismembered than the 

 other species with which it is associated. 



This species is quite unlike any other known to me in our formations, 

 though presenting, in its septa, some general resemblance to G. Chemungensis. 



Formation and locality. This species occurs in the same association with G. 

 Ixion, in the Goniatite limestone, at Rockford, Indiana. 



