44 LINDSTRÖM, A SPECIES OF TETRADIUM FROM BEEREN EILAND. 



ted at irregulär intervals, thus forming loose fasciculated coralla 

 resembling forms of Syringopora.» Then he describes (1. c. p. 

 238) his Tetradium apertum in the following manner: »Tubes 

 isolated or fasciculated, or eise united in linear series which often 

 intersect, forming irregulär reticulations.» He discerns two varie- 

 ties, but he also says that they appear to run into eacb other. 

 The variety a »Masses composed of separate tubes occasionally 

 united by their sides.>:' h ^Masses composed of tubes arranged in 

 linear series, the latter intersecting and forming raasses like those 

 of Halysites catenulatus Lin.» 



As I have told above, in the Beeren Eiland specimen both 

 these supposed varieties are found united in the same hand piece. 

 In other respects it also seems to stand in close affinity with 

 Safford's Tetr. apertum. It has been found only in a small 

 piece of the black limestone of only five centimetres in the 

 longest diameter. The size of the tubes near the apertures 

 amounts to 0,7 millimeters in the longest diameter. For these 

 isolated tubes are rather oval in some specimens, in others again 

 nearly square as Safford's fig. 1. They are of cruciform out- 

 lines, as the tube is indented at those points where the pseudo- 

 septa Stretch inwards. Interiorly the tubes are entirely converted 

 into a fine, crystalline mäss, showing no trace of the tabulae. 

 To conclude: if not absolutely identical with Safford's Tetra- 

 dium apertum it is so nearly related that it may be regarded 

 as a variety of that species. 



As to the systematic place of the genus Tetradium I can 

 here only refer to what I have said in my memoir on the He- 

 liolitidae^), with which fossils they, according to my opinion, not 

 have the slightest affinity. Nor can the exteriör resemblance of 

 this particular Tetradium apertum with Syringopora be adduced 

 as a convincing evidence of their affinity, as the Tetradium in 

 well preserved specimens have the tubes provided with regulär, 

 horizontal tabulae and not funnelshaped ones as the Syringopora?. 

 It is also difficult to see, why it should be placed in the neigh- 

 Remarks on the Heliolitidje. K. Sv. Vet. Ak. Handl. Bd. 32, N:o 1, p. 29. 



