SvA. NAT., TOL. XIT. 
VznnvAJiV, 1933 . 
By Bertiurd C. CoUan. 
61 . 
-centre of the shell and out at the other side, when the animal re- 
mains dextral and the shell is virtually sinistral. Another 
disease results in loose coiling, and in extreme cases the whole 
shell, normally making say lialf-a-dozen turns, makes only one 
or two (fig. 7). In addition there are many malformations due 
to fracture and repair during life. 
The last kind of Mollusca, the Scaphopoda are comparative- 
ly rare. They resemble an elephant’s tusk in shape, consisting of 
a slightly bent, gradually widening tube, ribbed or smooth, a 
scoop-like foot projecting at the wider end. 
Fig. 8. The Tusk Shell. 
The tubular shell, and the possession of a ribhon-Iike tongue 
suggests their relation with the Gastropoda, but the pointed foot, 
the disposition of internal organs, the absence of any definite 
liead and the structure of the embryo, approximates them to the 
Pelecypoda. Here is one of the mam^ Molluscan puzzles wait- 
ing to be solved. 
