PATAGONIAN EXPEDITIONS : PALAEONTOLOGY. 
(5 or 6), while even in smaller individuals (Nos. 12 and 13) a very high 
number (7 or 8) is present. 
Thus is seems that the number of sulci is very variable : at a length of 
ca. 50 mm. it is about 3, increasing at ca. 70 mm. to 4 and 6, and at over 
80 111m to 7 and 8, and even more ; but sometimes there are specimens, 
in which this number does not correspond to this rule : Sowerby’s figure 
23 shows an individual 47 mm in length, that has 5 or 6 sulci, where we 
should expect only 2 or 3, and v. Ihering’s individual of C. alta, of 45 
mm length, has 9, where we should expect not more than 3. Although 
this latter individual seems at the first glance to differ strikingly from 
all our individuals, Sowerby’s figure 23 and our specimen No. 9 form the 
transition between both extremes. 
Aside from the number of sulci on the area, v. Ihering (in 1899) gives 
the following differences between C. alta and dalli: (1) C. dalli is the 
larger species ; (2) the apex in C. alta is more anterior; (3) the surface 
ornamentation differs in both. 
Characters (1) and (2) are of no value, since there is in size and shape 
considerable variety, as is shown in our series : indeed, one of the largest 
specimens (No. 13) shows the apex more anterior than any of the rest, 
and this one agrees in all other respects with v. Ihering’s C. dalli. Further, 
it will be remarked that our No. 9, which, according to the sulci, is the 
one that approaches C. alta of v. Ihering most closely among our indi- 
viduals, shows an almost central apex, a character of C. dalli, and the 
same is true of No. 12. 
As to character (3), v. Ihering says that C. alta has in the middle of the 
shell ca. 30 radiating ribs, as broad as the intervals, but that these ribs 
are wanting on the anterior and posterior parts of the shell. In C. dalli, 
however, he says that these ribs are found all over the surface. (In 1897 
he described in C. dalli the surface-ornaments as striae rather than ribs.) 
It seems to me that he has not seen the original surface of the shell. 
In our specimens (see fig. 4 a ) — where the original surface is preserved — 
it is rugose (“subrugosa” Sowerby), i. e ., sculptured by very fine radiating 
striae or impressed lines, which are crowded, but some of them at certain 
intervals (3-10 mm) are a little more distinct (deeper). Ihe intervals 
between the striae are flat and crossed by fine undulating lines of growth : 
thus there is nothing that might be called “ribs.” But when the outer 
surface of the shell is destroyed by fossilization, the condition described 
