36 NILS HJ. ODHNER, MOLLUSCA. 
only we meet with forms fixed as Chamostrea with the anterior half of the right 
valve and the hinder half directed upwards (an attachment similar to that of Pseudo- 
chama cristella and P. retroversa) and that among the Anatinacea no pleurotethic 
forms exist which are similar to Chamostrea and speak in favour of its reference to 
this group. Even the animal of Chamostrea seems to repeat the conditions of Cham- 
ide by its reduced foot, its coalesced mantle, and the position of the gills (cf. An- 
THONY 1905). 
A close examination of the exterior and interior morphology of Chamostrea, 
for which I have taken the present specimens as subject, will show, however, 
: 
4 
é 
a 
oh i ty 
Fig. 5. Anatomy of Chamostrea plicifera n. sp., reconstructed from sections. a. aorta anterior; 
ad. adductor anterior; a. g. arteria gastrica; br. gill., c. g. cerebral ganglia; c. Zl. lateral coecal 
process; co. commissure between nephridia; h. heart; l. liver; l. c. liver canal; l. p, labial palps; 
n. nephroproct, in front of it genital pore; oe. oesophagus; p. g- pedal ganglia; p. ¢. pericardial 
tube of nephridia; Si, Sti anal and branchial siphons; st. statocyst; v. c. vena cava; 
v. g- visceral ganglion; v. p. vena pallialis; o’ male genital organs. 
that the resemblance to Chamidae is a mere parallelism and that the relationship 
must be sought in Anatinacea. 
The small valves of Ch. plicifera present in the collection allow an examination 
of the umbonal part of the free as well as the attached valves. If the form were 
a member of the Chamidae, we should expect to find its nepionic shell corresponding 
to that of a Pseudochama, i. e. to be of a rounded shape and furnished with widely 
separated projecting lamellae. But this is not the case; on the contrary, its outline 
is triangular, the umbones occupying the apex of the triangle, and its surface sculpt- 
ured with close thread-like concentric ridges, more distinct on the upper than on the 
lower valve. The nepionic shell thus resembles that of Myochama, a genus of Anat- 
inidae likewise confined to Australia and attached by its right valve. 
