71 
from a comparison with a young shell: here no marginal teeth of 
this kind are visible. Similar teeth, though fewer in number, are 
to be observed also in species of Gaimardia, e. g. G. acrobeles. 
The animal of Neogaimardia rostellata has its coalesced mantie 
edges pierced by three openings: a small pedal slit in the anterior 
sinus behind the rostrum, a long branchial one ventrally, and an 
anal opening behind. From Kidderia it dilfers in the mutual length 
of slits and sutures, and in the same respects it approaches Gai- 
mardia. Between the posterior slits which have both smooth mar¬ 
gins, like the pedal one, a pair of papillae are situated. 
The giils are reduced to comprise only one demibranch on each 
side, viz. the inner or anterior one, the posterior or outer gili plate 
being entirely obliterated. The demibranch has its filaments directed 
in the length of the body and is smooth, not plicated; both its 
direct and its reflected lamella are well developed. In both lamellae 
there are many interfilamentary junctions, but no interlamellary 
ones exist at all. The upper margin of the inner lamella contains 
a venous biood vessel and is fused to the body at the sides of 
the foot; both demibranchs likewise join their inner margins be¬ 
hind the foot. The posterior margin of the direct lamella represents 
the gili axis and is fused to the mantie in its whole length. Thus 
a spacious chamber occupies the interior of each demibranch, com- 
municating with the exterior only by means of the anal mantie 
opening; this room serves as a brood-pouch and was in many 
specimens filled with fry. 
The foot is furnished with a broad sole and contains a large 
byssus giand secreting a bristle of coarse byssus rods. In front 
of the byssus groove is a separate pore, the mouth of a mucus 
giand, quite as in Gaimardia. The retractor muscles of the foot 
are very strong. 
The pedal ganglia are situated far towards front. The statocysts 
at their upper sides contain one statolith each. 
At the sides of the broad mouth 2 pairs of well developed 
labial palps are present. The oesophagus is of moderate length. 
The cardiac portion of the stomach is produced on the left side 
to a slraight caecum; it is lined with a cuticule and receives one 
liver duet on each side. Downwards it passes on the left side 
into the pyloric sac lined with high ciliated epithelium. From the 
