688 CRETACEOUS PALEONTOLOGY. 



ately elevated spire, whorls three or three and a half, the outer 

 ones flatly truncate on the top adjacent to the suture line, the 

 truncation being strongly marked and angular at the margin. 

 On fully grown specimens it is nearly an eighth of an inch in 

 width on the outer half of the last volution; aperture oblique, 

 ovate, widest below and truncated above by the flattening of the 

 upper surface of the volution; umbilicus, as seen in the casts, 

 small, indicating a slender, almost if not entirely solid columella ; 

 margin of the umbilical depression not angular; surface of the 

 shell, as seen on fragments remaining attached to the casts, 

 marked by fine tranverse lines of growth." (Whitfield.) 



The dimensions of a large individual are : maximum diameter, 

 23 mm.; height, 20 mm.; height of aperture, 17 mm.; width of 

 aperture, 13 mm. 



Remarks. The original type of G. altispira has apparently been 

 lost or destroyed, but there are in the collection of the Philadel- 

 phia Academy of Science, several specimens labeled "duplicate 

 types" in G abb's own handwriting, which must be taken as 

 authentic representatives of the species. These specimens are 

 certainly specifically identical with the type of G. obtusivolva, 

 preserved in the same collection. These two species were de- 

 scribed at the same time by Gabb, but the species altispira precedes 

 obtusivolva, and consequently that name takes precedence. The 

 specimen which Whitfield has illustrated as an example of G*. 

 altispira is apparently only a member of the species. Lunatia halli. 



As observed in the recent collections of the Survey, this species 

 is restricted to the Merchantville clay-marl, and, judging from 

 their lithologic characters, the types of G. altispira and G. obtusi- 

 volva are apparently from this formation also. The species differs 

 from the associated G. crenata in the much smaller umbilicus and 

 narrower shell, in the absence of the subcarinate lower surface of 

 the volutions, and in the absence of the conspicuous crenate band 

 above. The species differs from Lunatia halli in the lower spire 

 and in the truncate upper surface of the volutions adjacent to the 

 suture. The species differs from G. petrosa in its proportionately 

 greater height, the less spreading or patulose outer volution, the 

 more elevated spire and the smaller umbilicus. 



