LOWER CRETACEOUS FOSSILS — ETHERIDGE. 155 



therefore, allowing for the full venter, dorsum, etc., must have 

 been considerable. 



The limb, or shaft, always has a laterally compressed or 

 flattened outline, giving it a " lean " appearance, except in an 

 instance to be noted immediately. The relation of limbs of this 

 nature to the coiled portions is satisfactorily shown in a specimen 

 from the Queensland Museum (PI. xl., figs. 1, 2). 



The costse are more or less always sigmoidal on the flanks, 

 often strongly so, frequently bifurcate, the points of bifurcation 

 being either low down on the flanks, supra-dorsal to all intents 

 and purposes, or along the middle line. The former occur on 

 the flanks of the whorls usually, and the latter on the shaft ; at 

 these points the costsa are not tuherculate. These subdivided 

 costse may, or may not, pass over the venter singly : when not so 

 doing they are gathered into fasciculate bundles along the 

 rounded abdominal margins by the prominent tubercles. A 

 fasciculus of three or four costse on a flank may be continued 

 across the venter as two costte only, and per contra, a similar 

 bundle on the latter maybe represented on a flank simply by two 

 also. A specimen in the National Museum, Melbourne, displays 

 a marked departure from the typical condition of the costa?, in 

 that many of the flank ribs are single, but on the venter between 

 the two rows of tubercles all are double. The appearance of the 

 tubercles is also worthy of note, in that the}' are cristiform, or 

 longitudinally elongated on the whorls, other than the youngest, 

 becoming more mammillary on the shaft and crozier. 



I received from the Geological Survey of Queensland a portion 

 of a large whorl measuring thirteen inches long by four inches in 

 diameter, but in a poor state of preservation. In comparison to 

 its size, the venter is not wide, but decidedly convex, although 

 the flanks are by no means so. The dorsum is costate, without 

 an impressed zone, and rather flat. The costae are very large, one 

 inch apart from crest to crest, straight and simple on the flanks, 

 curved forwards on the dorsum, and directly transverse on the 

 venter and double, the single line of nodes on each side separating 

 these double costa? from the single on the flanks. This may be a 

 condition of C. Jiindersi, like the smaller example already referred 

 to as in the National Museum, Melbourne, one in which the 

 fasciculate condition of the costae on the flanks has not been 

 developed ; this opinion, however, is expressed with all reserve. 



I now wish to draw attention to three marked conditions of 

 costation, indicating its variability notwithstanding a fundamental 

 resemblance throughout the whole suit of specimens. 



