wHiTEAVEs.J FOSSILS OF TRIASSIO ROOKS OF BRITISH COLUMBIA. 139 



in a specimen whose maximum diameter is fourteen millimetres, the 

 umbilicus is about six mm. in width and the inner volutions are partly 

 exposed. In adult specimens the outer volution is so closely embracing 

 that the whole of the inner whorls are covered. Sides of the outer 

 volution narrowing rajjidly and convexly from the umbilical margin 

 to the perij^hery, which latter is somewhat obtusely but very distinctly 

 angulated. Aperture very narrow in a dorso-ventral direction, angu- 

 lar above, widening rapidly and convexly to the base, which is deeply 

 and broadly emarginated by the encroachment of the preceding volu- 

 tion. If measured in the centre, where the emargination is deepest, 

 the heitfht of the apertui'e is not more than one-half of its maximum 

 length, but if measured outside of the emargination its height is a little 

 greater than its breadth 



Surface nearly smooth, marked only by rather distant but somewhat 

 irregularly disposed and very indistinct spiral striations, which are 

 crossed by almost equally indistinct and very slightly elevated trans- 

 verse plications. The faint revolving striiis are most strongly marked 

 on the outer half of the sides and become obsolete near the umbilical 

 margin, while the low, transverse plications or wrinkles are usually, 

 though not always, nearly straight and widen outwards towards the 

 periphery, over which they do not pass. 



Sutural line consisting of six simple saddles on each side of the sipho- 

 nal saddle, and of six simple lobes on each side of the siphonal lobe. 

 The apex of the very small siphonal saddle has a minute notch in the 

 centre, but all the other saddles ai'c quite entire at their margins. 

 The siphonal saddle is less than half the height of the first and second 

 lateral saddles, which are larger tjian the rest and about equal in size 

 to each other and to the corresponding lobes, while the third, fourth, 

 fifth and sixth lateral saddles are all very small and much shorter 

 than the first or second. All the lobes are minutely incised at their 

 margins. The siphonal lobe, which is rather deeply emarginated in 

 the centre by the small siphonal saddle, is broader but not quite so 

 high as the first lateral lobe, which latter is a little higher than the 

 second. The third, fourth, fifth and sixth lateral lobes are all very 

 small and much shorter than the second. 



The septa are closclj- approximated, and as the sutural lines of only 

 two or three contiguous septa are visible in specimens in which a not 

 inconsiderable portion of the outer lip is broken off, it seems clear that 

 when perfect the chamber of habitation must have been large and that 

 it must have occupied fully the whole of the outer volution. 



Dimensions of the largest undistorted specimen collected : maxi- 

 mum diameter, fifty-one millimetres ; greatest breadth or thickness, 

 twenty-seven mm. and a half; width of umbilicus, six mm. In a 

 December, 1888. 11 



