ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
417 
true. But if the relationships discovered are with typical marine genera, 
then there will be little doubt that the Halolimnic group originated in 
the lake through marine contamination. Of this, there is no direct 
evidence ; but there is no positive geological objection to the view that 
it has occurred, and there is at least evidence of great geological insta- 
bility in the districts concerned. In another paper, the author goes 
on to consider the structure and affinities of some of the Gastropods. 
Typhobia.* — Mr. J. E. S. Moore gives the first anatomical descrip- 
tion of this mollusc, “ probably the most remarkable freshwater Gastro- 
pod at present known.” It is fairly abundant in Tanganyika. 
The genus, which Fischer referred to the Melanias, must be dis- 
sociated from them, at least from all those which have been carefully 
examined. The nervous system is quite unique ; no relation with any 
other freshwater forms can be made out, but there is some suggestion 
of Solarium and the Scalarids. The Typhobias can hardly be called 
archaic, but they “ appear to be among the survivors of some old, but 
not geologically ancient, marine types.” 
Two forms are recognised, Typhobia Horei and Bathanalia Sowesi 
g. n., and a new family Typhobiid 2 e is proposed. They have affinities 
with and stand in the relation of forerunners to those more modern 
forms which group themselves about the Strombidte. They have also 
some of the characters of the Aporrhaidae, Xenophoridse, Cypraeidae, and 
Ptenoglossa. “ Their affinities show that they have without doubt been 
cut off from an exclusively marine stock at what is, geologically speak- 
ing, no very remote period of time.” 
Peripheral Glandular Organ of Helcion pellucidum.t — Prof. L. 
Bontan has much that is interesting to say in regard to this beautiful 
little mollusc, but we must confine our report to what forms the bulk 
of the paper, — an account of a peripheral glandular organ situated 
between the mantle and the foot, and interrupted only below the mouth. 
Like other skin-glands in Molluscs, it consists of a network of support- 
ing cells among which the glandular elements lie. The latter are 
of enormous size. The organ is formed as a longitudinal groove, the 
upper margin bounded by tentacles innervated from the pedal ganglia. 
It is not homologous, in position or innervation, with the epipodial 
“ collerette ” of Aspidobranchs ; it is homologous with a similar organ 
in Nacella, Patina , &c. ; and approaches the glandular tract in Chitons. 
As to function, it is probably at once sensory and defensive. 
5. Lamellibrancliiata. 
Are there Septibranchiate Bivalves PJ— Herr L. Plate criticises 
Pelseneer’s conclusion that the thick muscular septum which divides 
the mantle-cavity of Cuspidaria and Poromya into two chambers arises 
from the gills, and warrants the term “ Septibranchiate.” Plate seeks 
to show that the septum is not morphologically branchial or ctenidial, 
but rather pallial. He rejects the term “Septibranchiate” as applicable 
to Cuspidaria and Poromya, and proposes to call the group Septipalliata. 
* Quart. Journ. Micr. Sci., xli. (1898) pp. 181-204 (4 pis.). 
f Arch. Zool. Exper., v. (1897) pp. 436-82 (1 pi. and 10 figs.). 
X SB. Ges. Nat. Freunde Beilin, 1897, pp. 24-8. 
