314
KOHNAN Y. ARAKAWA
and the pellet consists of compacted detritus. The ends are usually
flattened and, at times, may have a small boss at the centre. The superficial consistency is fine and homogeneous. The ratio of length to
breadth of the pellets is usually smaller than 1.0.
Pellet-type 2. Ellipsoid
Pellet-type 2 occurs in two families of Gastrotetartika ; Galeommatidae (Scintilla) and Erycinidae (Lasaea), as well as in three families of
Gastropempta ; Semelidae (Abra and Theora), Mactridae (Mactra) and
Psammobiidae (Soletellina). This type of pellet is elongate elliptic in
shape. The surface is normally unsculptured but occasionally feebly
marked with a spiral striation (Mactra) or with segmentation (Scintilla).
The ratio of length to breadth of pellets is usually greater than 2.0.
IA. OVAL-ROD
Pellet-type 3. Constricted rod
This type of pellet is produced by four families of Gastropempts,
namely the Cardiidae (Cardium, Fulvia and Laevicardium), Solenidae
(Solen), Veneridae (Protothasa) and Mactridae (Schizothaerus and
Tressus). It can be distinguished by the rod-like form with a definite
linear segmentation. This type of pellet varies considerably in shape,
even in the pellets shed by the same animal in a short time ; they are
normally produced in the form of a rod marked with deep transverse
constrictions at regular intervals or occasionally secondarily separated
into ovoid pieces with truncate ends. They may have a single spiral
striation as in the case of Schixothaerus (Mactridae). Starvation tends
to produce the softer and more evenly surfaced continuous rod.
11. ROD
This category comprehends five distinct types and three varieties,
each of which can be distinguished structurally according to the
number, position and course of the grooves on the surface. It occurs in
all of the Protobranchia, some of the Gastrotetartika and Gastropempta.
Pellet-type 4. Plain rod
This type of pellet shows the simplest structure, being a plain rod
rounded in section. It is probably produced by two families of Gastrotriteia (Limopsidae and Spondylidae), five of Gastrotetartika (Chamidae, Laternulidae, Thraciidae, Lyonsiidae and Donaciidae) and six of
Gastropempta (Veneridae, Tridacnidae, Petricolidae, Corbiculidae,
Novaculidae and Corbulidae).
KOHNAN Y. ARAKAWA
and the pellet consists of compacted detritus. The ends are usually
flattened and, at times, may have a small boss at the centre. The superficial consistency is fine and homogeneous. The ratio of length to
breadth of the pellets is usually smaller than 1.0.
Pellet-type 2. Ellipsoid
Pellet-type 2 occurs in two families of Gastrotetartika ; Galeommatidae (Scintilla) and Erycinidae (Lasaea), as well as in three families of
Gastropempta ; Semelidae (Abra and Theora), Mactridae (Mactra) and
Psammobiidae (Soletellina). This type of pellet is elongate elliptic in
shape. The surface is normally unsculptured but occasionally feebly
marked with a spiral striation (Mactra) or with segmentation (Scintilla).
The ratio of length to breadth of pellets is usually greater than 2.0.
IA. OVAL-ROD
Pellet-type 3. Constricted rod
This type of pellet is produced by four families of Gastropempts,
namely the Cardiidae (Cardium, Fulvia and Laevicardium), Solenidae
(Solen), Veneridae (Protothasa) and Mactridae (Schizothaerus and
Tressus). It can be distinguished by the rod-like form with a definite
linear segmentation. This type of pellet varies considerably in shape,
even in the pellets shed by the same animal in a short time ; they are
normally produced in the form of a rod marked with deep transverse
constrictions at regular intervals or occasionally secondarily separated
into ovoid pieces with truncate ends. They may have a single spiral
striation as in the case of Schixothaerus (Mactridae). Starvation tends
to produce the softer and more evenly surfaced continuous rod.
11. ROD
This category comprehends five distinct types and three varieties,
each of which can be distinguished structurally according to the
number, position and course of the grooves on the surface. It occurs in
all of the Protobranchia, some of the Gastrotetartika and Gastropempta.
Pellet-type 4. Plain rod
This type of pellet shows the simplest structure, being a plain rod
rounded in section. It is probably produced by two families of Gastrotriteia (Limopsidae and Spondylidae), five of Gastrotetartika (Chamidae, Laternulidae, Thraciidae, Lyonsiidae and Donaciidae) and six of
Gastropempta (Veneridae, Tridacnidae, Petricolidae, Corbiculidae,
Novaculidae and Corbulidae).