NATURAL HISTORY SOCIETY OF GLASGOW. 167 



Between each pair of cells, in a longitudinal series, 1 to 3 pores 

 occur, normally above each cell aperture, and in well preserved 

 specimens tubercules surround each cell-area more or less 

 completely. 



The genus Sidcoretepora was founded by D'Orbigny in 1847, 

 with the following definition : — " Cells in series in furrows on one 

 side of simple depressed branches." In the genus thus defined 

 have been included, since 1847, species having the cells dispersed 

 all round the stems. 



To this genus are referred the following species found in the 

 Glasgow district, viz. : — S. parallela, Phil., S. raricosta, M'Coy. 

 The species above described differs from all those previously 

 recorded, by its small size, circular section, dichotomy, and surface 

 ornamentation. We have pleasure in naming it after Mr David 

 Eobertson, F.L.S., F.G.S., to whom we owe the loan of some of 

 the specimens figured. 



The cells are not always equally distributed round the stem ; 

 thus stems, usually the thicker ones, may have the cells on one 

 face fewer and smaller, and even reduced, as in fig. 1, to orifices 

 not larger than those already referred to as pores. Again, as 

 in fig. 8, the cells may be of unequal size, the pores remaining 

 equal. This is most frequent near the points of bifurcation where 

 new rows become intercalated between those of the stem. We have 

 already described and figured Carboniferous Polyzoa ^ in which 

 pores occur in the longitudinal series, as in Glaucoiiome stellijjora and 

 Actinostoma fenestratum. The present species seems to render more 

 probable the avicularian character of these orifices, every gradation 

 of aperture being seen, from the cell slightly smaller than usual, 

 down to pore-like openings. Further, the tubercular ridges which 

 bound the cells are, as in figs. 3, 5, and 11, seen to surround 

 small cell apertures and also the intercellular pores. No ovicells 

 are to be recognised. 



S. Bohertsoni is moderately common in a thin bed of light-grey 

 shale (Lower Limestone series) at Trearne, near Beitb, but the 

 specimens are somewhat worn. Fragments have been found in 

 shale at Brockley near Lesmahagow, and at Auchenskeoch near 

 Dairy, but at both these localities the species seems to be rare. 



* Quart. Journ. Geol. Soc. Lond., Vol. xxx., p. 681. 



