VIl] 



BACTRYLLIUM. 



155 



by Heer* from the Trias of Switzerland and North Italy, also 

 from the neighbourhood of Heidelberg, and regarded as an 

 extinct member of the Diatomaceae. Heer defined the genus 

 as follows : 



" Small bodies, with parallel sides, rounded at either end, the surface 

 traversed by one or two longitudinal grooves." 



(fig. 32, C.) Several species have been figured by Heer from 

 beds of Muschelkalk, Keuper and Rhaetic age. He describes 

 the wall as thick and firm (fig. 32, C. ii.) and probably com- 



(i) 



B 



Fig. 32. A, Lithothamnion mamillosum Giimb. (i) In section, (ii) surface view 

 [after Giimbel. (i) x 320, (ii) nat. size]. B, Sycidium melo Sandb. 

 (i) Surface view, (ii) transverse section (after Deecke). C, Bactryllium 

 deplanatum Heer. (i) Surface view, (ii) section, showing the thick wall 

 and hollow interior (after Heer). D, Calcareous pebble from a lake in 

 Michigan. Rather less than nat. size (after Murray). 



posed of silica, with a hollow interior. The specimen shown in 

 fig. 32, C. was found in the Rhaetic beds, and named by Heer 

 Bactryllium deplanatum; it has a length of 4"5mm. ; the 

 surface is transversely striated and traversed by a single longitu- 

 dinal groove. Stefani^ has given reasons in favour of removing 



1 Heer (76) p. 66, PI. xxiii. and (53) p. 117, PI. vi. 

 « Stefani (82) p. 103. 



