On neto 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 liesitated 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 Edgar A. Smith. 



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 Neothauma 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 Spekei^ Woodward, Spatlia tang any icensis, Smith, 

 and Unio Burtoyii^ Woodward, fresh specimens of Limno- 

 trochus Kirki but without opercula, a large form of L. Thorn- 

 soni, and a large, solid, tabulated variety of the ever variable 

 Paramelajiia 7iassa. Taking tlie 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 Graudidier, Bull. Soc. Mai. France, vol. ii. pp. 162-164 ; Bour- 

 guignat, Mull. terv. et lluv, dii lac Tiuigauyika, l8Bo, pp. 2o-!^'9, 



