imperfectJy-kiwnin Sjyecies of Stromatoporoids. Vi^ 



Tangential sections (woodcut, fig. A) show that the radial 

 pillars are holloWj each being traversed by a well-marked axial 

 canal. The tissue forming the periphery of the pillars is 

 composed of very delicate laminae which surround the axial 

 canal concentrically, and which often show a minute cribri- 

 form structure. The connecting processes spring from this 

 tissue, and can commonly be followed in vertical sections for 

 a considerable distance into the substance of the pillars. 

 Tangential sections further exhibit irregular dark lines con- 

 necting the transversely divided tangential pillars ; these 

 lines are the cut edges of the vesicular plates or processes 

 which fill the intervals between the pillars. 



There is, apparently, a complete absence of definite zooidal 

 tubes or surface apertures, and the " concentric laminaj " of 

 the ordinary Stromatoporoids are represented solely by the 

 vesicular tissue which unites the pillars together. 



Formation and Locality. Abundant in the Wenlock Lime- 

 stone of Britain (Ironbridge, Dudley, Dorraington, Longhope, 

 &c.). I have also specimens from the Wenlock Limestone of 

 Gotland (presented to me by Prof. Lindstrom) ; but I have 

 not obtained the species in the Silurian deposits of Esthonia 

 or Oesel. 



LahecMa okioensisy Nich. (PI. II. figs. 1 and 2.) 



Lahechia ohioensis, Nicholson, Men. Brit. Strom, p. 32, footnote, pi. ii. 



figs. 1 & 2 (1885). 

 Lahechia montifera, Ulricli, Contributions to American Palseontology, 



vol. i. p. 33, pi. ii. figs. 9, 9a (1886). 



Coenosteum sometimes laminar and pedunculate (?), often 

 encrusting foreign bodies. Upper surface sometimes smooth, 

 but more commonly with small conical " mamelons," covered 

 throughout with minute rounded or pointed tubercles. Hadial 

 pillars about ^ millim. in diameter, and placed at distances of 

 from I to -1- millim. apart. The radial pillars are mostly more 

 or less angulated, and sometimes exhibit distinct traces of axial 

 canals. The interspaces between the pillars are occupied by 

 delicate vesicular tissue formed of minute vesicles, the con- 

 vexities of which are directed towards the surface. 



Ohs. In general structure this well-marked species resem- 

 bles L. conferta, Lonsd., sp. It is distinguished from this, 

 however, by the much smaller size of the radial pillars, and the 

 correspondingly smaller and less prominent tubercles upon the 

 surface. Moreover, the pillars commonly appear angulated or 

 stellate in cross-section instead of being round or oval. Lastly, 

 the vesicles of the interstitial tissue are much smaller and more 

 delicate, and are developed in proportionally greater quantity 

 tlian is the case in L. conferta (PI. II. fig. 1). 



