326
KOHMAN Y . ARAKAWA
shape of an inverted ‘ V’ in section. There is a slight mid-dorsal
thickening corresponding to the mid-dorsal ridge of Mytilus, and the
lateral regions are thickened as in that species, but here the edges are
very much narrower and are not turned up. The ribbon is formed from
similar fine detritus, but there is no such localization of materials, and
it appears homogeneous in transverse section. From an animal 10 cm
long, the ribbon averages 2.0 mm in diameter, and is often in lengths
of two or more centimetres.” (Moore, 1931, p. 283, PI. 31, Pigs. 11, 12,)
(Pellet-type III-lOa.)
29. M . phuseolinus (Phi1ipp)i
“ The pellet is somewhat intermediate in form between those of
the previous two species (Mytilus edulis and Modiolus modiolus). The
mid-ventral groove is much smaller than in M . modiolus, and though
sometimes deep, it is always narrow, and may even be completely
closed ; also in this species the mid-dorsal ridge is a wide thickened area
of the ribbon. The lateral regions are relatively longer than those of
M . modiolus, though not so long as those of Mytilus, and are thickened
at the edges, The pellet is composed of fine detritus, but unlike that
of M . modiolus, there is here a sorting of the finer material to the
lateral regions of the ribbon, and of the coarser materials to the centre.
The ribbons may be several centimetres long, but when the animal is
feeding normally they usually break into very short lengths.” (Moore,
1931, p. 283, PI. 31, Figs. 1 1 , 12.) (Pellet-type 111-lOa).
30. M . ugripetus (Iredale) (PI. 5-54)
Ribbons are usually shed broken into short lengths (1.0-1.5 times
as long as wide). A low and broad median rib lies on the dorsal side,
while orl the other side is a shallow and indistinctive mid-ventral
groove. They are very fine in texture, rather stiff in consistency and
brownish-grey in colour (Pellet-type III-l0u).
Locality : Mukaishima, Hiroshima, Japan.
Measurements: For an animal with 11 mm long shell, the ribbons
average 0.31 mm in width.
31. M . nipponicus (Oyama) (Pl. 1-5)
The free
edges of the ribbons slightly turn dorsalwards. There is a low median
rib on the dorsal side and on the opposite side to this, a shallow and
narrow longitudinal groove (Pellet-type III-l0a).
Pellets are ribbon-shaped with a bi-crescentic section.
KOHMAN Y . ARAKAWA
shape of an inverted ‘ V’ in section. There is a slight mid-dorsal
thickening corresponding to the mid-dorsal ridge of Mytilus, and the
lateral regions are thickened as in that species, but here the edges are
very much narrower and are not turned up. The ribbon is formed from
similar fine detritus, but there is no such localization of materials, and
it appears homogeneous in transverse section. From an animal 10 cm
long, the ribbon averages 2.0 mm in diameter, and is often in lengths
of two or more centimetres.” (Moore, 1931, p. 283, PI. 31, Pigs. 11, 12,)
(Pellet-type III-lOa.)
29. M . phuseolinus (Phi1ipp)i
“ The pellet is somewhat intermediate in form between those of
the previous two species (Mytilus edulis and Modiolus modiolus). The
mid-ventral groove is much smaller than in M . modiolus, and though
sometimes deep, it is always narrow, and may even be completely
closed ; also in this species the mid-dorsal ridge is a wide thickened area
of the ribbon. The lateral regions are relatively longer than those of
M . modiolus, though not so long as those of Mytilus, and are thickened
at the edges, The pellet is composed of fine detritus, but unlike that
of M . modiolus, there is here a sorting of the finer material to the
lateral regions of the ribbon, and of the coarser materials to the centre.
The ribbons may be several centimetres long, but when the animal is
feeding normally they usually break into very short lengths.” (Moore,
1931, p. 283, PI. 31, Figs. 1 1 , 12.) (Pellet-type 111-lOa).
30. M . ugripetus (Iredale) (PI. 5-54)
Ribbons are usually shed broken into short lengths (1.0-1.5 times
as long as wide). A low and broad median rib lies on the dorsal side,
while orl the other side is a shallow and indistinctive mid-ventral
groove. They are very fine in texture, rather stiff in consistency and
brownish-grey in colour (Pellet-type III-l0u).
Locality : Mukaishima, Hiroshima, Japan.
Measurements: For an animal with 11 mm long shell, the ribbons
average 0.31 mm in width.
31. M . nipponicus (Oyama) (Pl. 1-5)
The free
edges of the ribbons slightly turn dorsalwards. There is a low median
rib on the dorsal side and on the opposite side to this, a shallow and
narrow longitudinal groove (Pellet-type III-l0a).
Pellets are ribbon-shaped with a bi-crescentic section.