464 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
Range of Placost.ylus.* — Mr. E. Hedley makes the geographical 
range of this snail a text for a study in ancient geography. He thinks 
that the area which it occupies should rank as a zoological province to 
be called Melanesia ; it would embrace the archipelagoes of Solomon, 
Fiji, New Hebrides, Loyalty, New Caledonia, Norfolk I. (?), Lord 
Howe I., and New Zealand. This area was never connected with nor 
populated from Australia, and its fauna was probably derived from 
Papua via New Britain. The presence of genera common to Australia 
and New Zealand is explicable by the supposition that they derive, in 
either case, from New Guinea as a common source. 
5. Lamellibranchiata. 
Ocular Nerves of Spondylus gcederopus.j — M. J. Chatin reminds 
the student that he has already demonstrated the existence, in the eyes of 
Pectens, of an optic nerve which supplies the retina, and of ophthalmic 
nerves which innervate the peripheral parts. These two kinds of nerves 
are found in Spondylus goederopus , where they arise separately from 
the circumpallial nerve. With osmic acid the optic nerve is stained 
black, while the ophthalmic nerves are hardly tinted at all. The staining 
is due to the presence of myelin, a very rare occurrence among Inverte- 
brates. 
Food of Oysters, Clams, and Mussels.! — Mr. J. P. Lotsy, on sucking 
out by a pipette the contents of the stomach, found an abundance of 
diatoms, but a total absence of Copepods, although these were very 
abundant in the surrounding water. Cultures of diatoms were taken by 
the animals, but hashes of Copepods were either refused at once, or, if 
accepted, were instantly rejected and that forcibly, being driven to a 
distance of six or seven inches. 
Pedal Impression of Pachyerisma.§ — Prof. G. Boehm points out 
that Pachyerisma bears a distinct impression of a pedal muscle on the 
under surface of the anterior lateral tooth, therefore P achy meg alodon 
cannot be separated from Pachyerisma , as Neumayr thought necessary. 
Lithiotis problematica Giimbel.||— Prof. G. Boehm finds that the 
fossils so named are oysters. Often only the ligament region remains. 
The frequent grooves in this region are due to weathering, and are also 
seen in Tertiary oysters. He finds further that Trichites Loppianus 
Tausch is an Ostrea , and near the so-called Lithiotis. The very 
numerous white bands and streaks in the grey limestone are not wholly 
sections of the above-mentioned oysters, but also due to Perna. 
Molluscoida. 
a. Tunicata. 
Origin of Metagenesis in Tunicata.lf — Prof. W. Salensky sums up 
the results of an interesting essay on this subject in the following 
terms : — 
* Proc. Linn. Soc. N.S.W., vii. (1893) pp. 335-9. 
f Comptes Rendus, cxvi. (1893) pp. 1156 and 7. 
X John Hopkins Univ. Circ., xii. (1893) pp. 104 and 5. 
§ Ber. Nat. Gesell. Freiburg i. B., vi. (1892) pp. 119-20. 
|| Tom. cit., pp. 65-80 (3 pis.). 
Biol. Centralbl., xiii. (1893) pp. 126-46. 
