130 
Transactions of the Royal Society of South Africa. 
The percentages given by v. Hoepen are -34 — -17— 40 for an example of 
120 mm. diameter. The specimens range from 60 mm. (B.M., No. C 18521) 
to 145 mm. (C 18516) in diameter, and the relatively thickest form (C 18518) 
has a narrow umbilicus (dimensions : 130 — -34 — -215 —-40), whereas the 
thinnest form (C 18517) has a wide umbilicus (dimensions : 138 — -30— -16 
— •46). This, as Mr. Crick observes, is contrary to the general rule 
given by Grossouvre,* namely, that in the same specific type individuals 
with a narrow umbilicus show a corresponding compression of the 
whorls. 
The transverse section of an example 106-5 mm. in diameter (B.M., No. 
C 18520), very close to the type-specimen, allowed of measurements being 
taken at different stages, and Crick's figures are here appended : 
Diameter of 
106-5(1 ) 
78-0 (1 ) 
55-0 
(1 ) 
38-0 (1 ) 
26-0 (1 ) 
18-5 (1 ) 
12-75(1 ) 
shell 
Height of 
37-5 (0-352) 
29-5 (0-378) 
20-75 
(0-377) 
14-75 (0-388) 
10-0 (0-384) 
6-5 (0-351) 
4-5 (0-352) 
outer whorl 
Thickness of 
21-5 (0-201) 
16-5 (0-211) 
11-5 
(0-20 ) 
8-25 (0-218) 
5-75(0-221) 
3-5 (0-189) 
3-5 (0-274) 
outer whorl 
Width of 
41-5 (0-389) 
28-25 (0-362) 
19-5 
(0-354) 
13-5 (0-355) 
10-0 (0-384) 
6-75 (0-364) 
4-5 (0-352) 
umbilicus 
The same transverse section shows that at a diameter of 13 mm. there is 
no keel, whereas at 18 mm. it first begins to be indicated very feebly. Up 
to a diameter of 50 mm., the constrictions, also, are biconvex, like those of 
H.fayoli, Grossouvre, or of Forbes 's small types of H. rembda { = A. durga). 
The course of the constrictions, if it remains biconvex in larger examples of 
H. rembda, as drawn by Stoliczka,f may serve as a distinction between the 
two species, as, e.g., Pervinquiere J had thought ; for the larger whorls of 
H. gardeni have semicircular constrictions, sloping forwards towards the 
umbilical suture as much as the outer half is projected forwards towards 
the keel. In several examples the apex of this semicircular curve is 
slightly flattened ; in others there may be a small indentation in the semi- 
circle, either near the umbilical edge (No. C 18540) or nearer the periphery 
(C 18537), suggestive of the original biconvexity, and in the transitional 
stage the course of the constrictions would be as described for H. sulcatus 
by Kner and Nowak.§ 
The last example has the periphery of the cast (but not that of the test) 
still rounded at a diameter of 110 mm., as in Baily's larger specimen (No. 
11371, Geol. Soc. Coll.). Another example (C 18522) has lateral grooves 
* Loc. cit. (1894), p. 8. 
f Loc. cit. (1864), pi. xxxiii, fig. 5. 
t Loc. cit, (1907), p. 169. 
§ Kner, " Verstein. d. Kreidemerg. v. Lemberg.," Naturw. Abh., iii (1850), 2, p. 8, 
pi. i, fig. 3 : and Nowak, loc. cit., p. 371, pi. xli, fig. 12, pi. xlv, figs. 44-45. 
