134 NOTE ON "CRIOCERAS AUSTRALE," 



Ho *vever, some of the characters of the genus will be sufficiently 

 illustrated, namely : — The septa divided into six lobes, the dorsal 

 lobe only being formed of a par number of divisions, the other 

 lobes formed, in general, of an impar number of divisions; and the 

 dorsal siphuncle. 



The description given by Chas. Moore deserves to be quoted 

 beforehand. 



" Shell very large, discoidal ; whorls rounded , incurved, the 

 " inner whorls rather closely fitting but separate. In the younger 

 " state, as seen in the reduced figure, the shell possesses regular 

 11 rounded slightly curved ribs with intervening rounded sulci, 

 " which increase in width with the age of the shell. In the adult 

 " shell the ribs become widely separated, the largest chamber 

 " measuring at the back 3^ inches, and they possess very acute 

 " ridges, with two depressed bosses on either side, the depression 

 " between the ribs being regularly concave." 



" The block containing the last five chambers of the shell is 

 " slightly compressed on the back ; and, though it is not complete, 

 "the mouth measures 7^ inches in depth by 7 inches in breadth. 

 " The siphuncular tube is small and situated immediately under 

 " the back of the shell," (loc. cit. p. 257). 



The elements of the measurements in the specimen here repre- 

 sented (PI. 2) approximately are as follows : — 



Maximum diameter, 28^ in. 



Thickness of the last whorl, 10 to 12 in., or at least ^ of the 

 above diameter. 



The thickness, in the larger whorls, seems to be, as observed by 

 Mr. Moore, larger than the width, therefore, the excentricity 

 (— thSness) which, for the smaller whorls is about constant and of 

 ™, would, thus be reversed in the larger ones, but it has been 

 impossible to measure it owing to the imperfect state of the fossil. 

 Compared with the width of the shell the space between the ribs 

 at the back is about ^,, for the smaller whorls represented and for 

 the external ones, but it increases considerably towards the 

 aperture being about ^ in the last coiled whorls and ^ or more in 

 the largest part that it has been possible to measure. 



