THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[FOURTH SERIES.] 

 No. 117. SEPTEMBER 1877. 



XXI. — Contributions to Micro-Palmontology . — I. On the Genus 

 Tetradium, Dana, and on a British Species of the same. 

 By H. Alleyne Nicholson, M.D., D.Sc, F.E..S.E., and 

 Robert Etheridge, Jim., F.G.S. 



Genus Tetradium, Dana, 1846 

 (Wilkes's Expl. Exped. Zoophytes, p. 701). 



The genus Tetradium was founded by Prof. Dana for the 

 reception of a fossil of uncertain locality in the collection of 

 Yale College, New Haven 5 and the following characters were 

 ascribed to it : — " Coralla massive, consisting of four-sided 

 tubes and cells, with very thin septa or parietes ; cells stellate, 

 with four narrow laminae." 



At a subsequent date, Prof. J. M. Safford described four 

 species of corals from the Lower Silurian rocks, which he 

 referred to this genus (Amer. Journ. Sci. and Arts, ser. 2, 

 vol. xxii. p. 236); and he supplemented Dana's description with 

 the following remarks : — " The tubes in the different species 

 vary from one quarter of a line to nearly one line in breadth ; 

 they are very long, and are most frequently united tlirougliout 

 laterally, forming massive coralla, resembling more or less those 

 of Favosites and ChcBtetes ; sometimes, however, they are 

 united in single intersecting series, as in Halysites catenulataj 

 Linn. ; not unfrequently, too, the tubes are isolated, or only 

 united at irregular intervals, thus forming loose fasciculated 

 coralla, resembling certain forms of Syringopora.^^ 



Ann. & Mag. N. Hist. Ser. 4. Vol. xx, 11 



