RISSOA ZOSTEROPHILA (Risso, the naturalist; 
Zostera, the Seawrack, grass-like seaweed; philos, loving). 
—Commonly known as the Spire shell, this species, like all 
the Rissoas, is a very minute spiral univalve, one-six- 
teenth of an inch in height. The shell is horn-coloured or 
dark brown, with a broad white band below the suture, and 
the mouth, which is circular, is slightly to one side. It is 
found under stones between tide marks, or on the beds of 
seaweed, such as one sees growing on mud flats and in 
shallow water. This species is the only minute one included 
in these pages, for most people consider such small crea- 
tures as beneath notice; but as the Rissoa Zosterophila is 
fairly common, and easy to find, it is to be hoped that its 
introduction here may lead to the further study of these 
fascinating little molluscs. 
Auckland Harbour; Tauranga Harbour; Cook Strait; 
Lyttelton ; Taumaki. 
RISSOINA RUGULOSA (Rissoina, dim of Risso, 
the naturalist; rugulosa, having rugae or wrinkles) —A 
narrow tapering and elongated spiral univalve, about a 
quarter of an inch high, and less than an eighth of an 
inch in diameter. There are seven or eight whorls, and 
the shell is yellowish white, yellowish brown, or white in 
colour; hence they are familiarly known as “grains of 
rice.” The sculpture consists of axial ribs or wrinkles, 
fifteen or sixteen on the whorl above the body whorl. The 
ribs on the body whorl extend about half-way towards the 
base, or may be merely indicated just below the suture. 
The aperture is approximately a half-oval, and is about one- 
third the height of the entire shell. The upper end of the 
mouth is slightly channelled, and there is a small notched 
canal in the rounded base of the outer lip. Found on the 
under side of boulders at low tide. 
Bay of Islands; Hauraki Gulf; Mount Maunganui; 
Banks Peninsula; Stewart and Chatham Islands. 
CERITHIDEA BICARINATA (ceration, a small horn; 
bi, two; carinata, keeled).—A narrow tapering spiral uni- 
valve, the largest specimens being a little over one inch in 
length; of a blackish-brown or blackish-purple colour. The 
sculpture consists of prominent ribs, arranged longitudin- 
ally, with finer ribs, at right angles to them, occupying the 
intervening spaces. The name bicarinata is due to the 
two spiral carinae or ridges winding round the base of the 
last whorl. It is found in harbours and estuaries on mud 
banks, and is usually much encrusted and eroded. So 
much is this the case that the protoconch, or extreme tip 
of the spire, has never been seen except in juveniles of 
39 
Plate VIII 
No. 14 
Plate VIII 
No. 15 
Plate VIII 
No. 21 
Sea Shells 
of New Zealand 
