Suture —The line of union between one whorl and the 
adjacent one in a spiral univalve. 
Umbilicus.—A cavity, circular depression or chink at 
the base of spiral univalves, affording lightness and 
strength; not present in all. Those possessing it are 
termed perforate; those without, imperforate. 
Umbo (plural, wmbones)—The boss or rounded emi- 
nence of a circular shield. In bivalves, the umbo is 
the rounded and elevated portion adjoining the beaks, 
Varix (plural, varices) —A large rib, such as those on 
the Septa costata and the Murex Angasi var. Eos, 
descending down the whorls. They are usually few 
in number, and are so named in contradistinction to 
the ordinary longitudinal ribs on spiral univalves, 
which are numerous and of much smaller size. 
Whorl.—One complete turn of a spiral univalve; the 
lowest of all, with the aperture—z.e., the body whorl— 
containing the body of the animal. This is at the ante- 
rior end of the shell, as the animal, during its pro- 
gress, advances this portion of its shell in front. In 
describing the dimensions of a univalve, the word length 
denotes the distance between the tip of the spire and 
the extreme base; the word height signifies precisely 
the same dimension, but presumably in the empty shell, 
held in the hand with the spire naturally pointing up- 
wards. In the bivalve the height is invariably the dis- 
tance measured from the hinge to the opposite point 
of the ventral margin, the length being always the 
distance between the anterior and posterior borders. 
The length is not always the longest diameter: for in- 
stance, the Lima bullata is only half as long as it is 
high. 
123 
Sea Shells 
of New Zealand 
