1899] BOMBARDIER BEETLES 423 



Aii old Link between North America and Arctic 



Europe. 



Tetradium is the name given by Dana to a Palaeozoic fossil of some- 

 what uncertain affinities, but apparently a coral. The presence of 

 four septa, forming an aperture shaped like the diaper of Gothic 

 architecture, and of grooves or rugae outside the tubes and exactly 

 opposite the septa, are features reminiscent of the Eugosa. A certain 

 connection of the calicular tubes through intervening lamellae induces 

 a superficial resemblance to the chain-coral — Halysites. Some of the 

 species grow in compact masses, the tubes in close contact ; in others, 

 such as T. apertum, the tubes are further apart and united laterally 

 only by horizontal tubules such as occur in Syringopora, a genus from 

 which it differs in all other respects. 



Tetradium has hitherto been known only from the Ordovician of 

 North America, being confined to the Trenton and Hudson Eiver 

 groups of Tennessee, Kentucky, Ohio, New York, and Canada. 

 Attempts have, it is true, been made to record it from elsewhere. 

 Nicholson and Etheridge described a Tetradium peachi from the 

 Scottish Silurian, but it does not present the characters of the genus. 

 Schlueter has shown that Freeh's Tetradium eifeliensc is only a 

 Calamopora. Last year, however, Professor A. G. Nathorst brought 

 back from Beeren Eiland, near Spitzbergen, fragments of limestone in 

 which Professor Gustaf Lindstrom has detected a Tetradium indis- 

 tinguishable from T apertum, Safford. He describes and figures it in 

 Ofversigt af k. Vetenskaps-Akademiens Forliandlingar ; 1899, No. 2. 

 This both extends the geographical range of the genus and proves the 

 existence of Ordovician limestone on Beeren Eiland. 



The Artillery of the Bombardier Beetles. 



The ejection of an acid fluid, which explodes and vaporises in contact 

 with the air, from the tail-end of carabid beetles of the genus 

 Brachinus is well known to entomologists. It seems to serve as a 

 valuable protection against the pursuit of larger members of the 

 family. Dr. L. Bordas has recently (Zool. Anzeiger, xxii. pp. 73-76) 

 studied the apparatus to which this secretion is due. A pair of 

 glands, consisting of bundles of lobules, are situated on either side of 

 the intestine beneath the dorsal body-wall ; from these lead long, 

 coiled efferent ducts, which are remarkable for the narrowness of their 

 internal diameter and the great thickness of their circular muscle- 

 layer which is arranged in a series of annular discs. Each duct 

 opens into a large reservoir, whence an ejaculatory duct arises to open 



