554 G. C. Crick — On Vestinautilus. 



the rest of the latter being only faintly indicated in section in the 

 matrix ; then follows a length of about 10 mm. of the antepenultimate 

 whorl, whilst the rest of the inner whorls are entirely covered by 

 matrix. The lateral aspect of the shell agrees very well with that 

 given by Dr. Foord {op. cit., pi. xxii, fig. 5a), allowance being made 

 for the elliptical form of the figured example. The fossil shows 

 the crenulated ornamentation of the young shell ; also the subsequent 

 spiral ridges occurring on both the lateral and the peripheral sides 

 of the prominent umbilical margin, and which, gradually disappearing, 

 leave only fine, well-marked transverse striae ; on the greater part 

 of the side of the whorl these strise are a little reclined ^ ; rising with 

 a backwardly-directed curve on to the umbilical margin, they cross 

 the peripheral area with a very distinct and deep, backwardly-directed 

 sinus, indicating the presence of the hyponomic sinus ^ of the 

 aperture. On the outer whorl of the specimen this sinus is some- 

 what deeper and narrower than Dr. Foord's figure (fig. 5b) represents, 

 but this seems to be due in part, but only in part, to the fact that 

 the latter half of the outer whorl has been somewhat compressed 

 laterally, sufficient, however, to force outwards the central portion 

 of the peripheral area and eventually to fracture it. Consequently 

 the median portion of the periphery of this part of the fossil is- 

 much more convex than is represented even in the lower part of 

 Di'. Foord's figure (fig. 56),^ in fact the two sides of the peripheral 

 area are inclined to each other at an angle of rather more than 100° ; 

 the peripheral area of the earlier and uncompressed part of the 

 whorl is, however, relatively less convex. Owing to the compression 

 already mentioned, the transverse section of the anterior end of the 

 outer whorl of the specimen is almost pentagonal in outline, and 

 the proportion of its dorso- ventral diameter (or height) to its transverse 

 (or width) is greater than shown in Dr. Foord's figure (fig. 5c), 

 the height, from the centre of the area of inclusion to the centre of 

 the peripheral area, being 35 mm., and the width, from the summit 

 of one umbilical rim to the summit of the other, 41-5 mm., the 

 corresponding dimensions given by Di". Foord, in an example 127 mm.- 

 in diameter, being 24 mm. and 44 mm. respectively. This pro- 

 portion is rendered greater than it would naturally be by the fact 

 that the test is imperfect on the umbilical rim on one side and 

 entirely wanting on the other. At the anterior end of the specimen 

 the siphuncle is seen, but owing to the compression of the whorl 

 it is not quite in the median line ; it is nearly 5 mm. in diameter, 

 its outer surface being 10 mm. below the centre of the periphery, 

 this being the position assigned to it by Dr. Foord ; the ' zone of 



1 In the coiled shell of a XJephalopod the ribs or striae are said to be 

 ' direct ' when their direction coincides with the radius ; ' inclined ' when they are 

 forwardly-disposed in relation to a radius ; and ' reclined' when they are backwardly- 

 directed in relation to the same line. 



2 The sinus of the apertui-e at the median part of the peripheral area or Tenter 

 indicating the position of the funnel or h^'pouome. 



^ It is to be noted also that the periphery in Dr. Foord's diagrammatic transverse 

 section of the whorl (fig. 5c) is much less convex than it is represented at either the 

 lower or the upper part of the front view of the fossil depicted in his fig. 6b. 



