On new Shells from Lake Tanganyika. 173 
sufficient evidence of the absurdity of supposing that because 
the Arachnida are terrible to women they must therefore be 
equally alarming to birds. 
The sting-like tentacles of the larva of Dicranura vinula 
are likewise no protection; three young Nightingales, which 
I had the year before last, never hesitated for a moment to 
use the tentacles as handles to assist them in knocking the 
life out of the caterpillar before devouring it. 
XX.— Diagnoses of new Shells from Lake Tanganyika. 
By Epaar A. SmItu. 
A SMALL series of shells from Lake Tanganyika has lately 
been purchased of Mr. Coode Hore by the British Museum. 
Among other interesting specimens are some very remarkable 
varieties of Neothawma tanganyicense, considerably larger and 
more finely developed than those originally described and 
showing also much variation in form. After careful consider- 
ation I cannot but regard all the five described species * of 
this genus as modifications of one and the same variable form. 
The collection also contains some very fine examples of 
Pleiodon Speked, Woodward, Spatha tanganyicensis, Smith, 
and Unio Burtont, Woodward, fresh specimens of Liémno- 
trochus Kirki but without opercula, a large form of LZ. Thom- 
soni, and a large, solid, tabulated variety of the ever variable 
Paramelania nassa. ‘Taking the extreme forms of the last 
species, it seems impossible to regard them as belonging to the 
same species ; yet in large series it becomes impossible to draw 
reasonable lines of specific limitation. Bourguignat in his 
absurd manner has already created twenty-three so-called 
species out of this remarkable shell ! 
Some specimens of Spekia zonata, Woodward, fortunately 
contain the operculum, which has not previously been 
observed. 
It has the appearance of being rather small in proportion 
to the size of the shell. It is of a long ovate form, concave 
externally, concentrically striated except near the central 
nucleus, where it is paucispiral. The lower surface has a 
smooth glossy margin, broader on one side than on the other, 
and the muscular impression is dull, ovate, and marked with 
concentric lines of growth. 
* Vide Grandidier, Bull. Soc. Mal. France, vol. ii. pp. 162-164; Bour- 
guignat, Moll, terr. et fluy. du lac Tanganyika, 1885, pp. 25-29. 
