imperfect^y-lcnown 8j)ecies of Stromatoporolds. 227 



zooids, and definite tabulate zooidal tubes are not present. 

 Astrorhiza3 are feebly represented or may be wholly wanting. 

 The surface is not furnished with regular eminences or 

 " mamelons." 



Ohs. This species is the one which has most generally been 

 identified with Stromatopora concentrica ., Goldf., though 

 various other species have been from time to time referred to 

 under the name of B. concentrica. The present species has 

 been more particularly identified with 8. concentrica, Goldf., 

 by Bargatzky * {'■ Stromatoporen des rheinischen Devons,' 

 p. 54). I have elsewhere pointed out, however (Mon. Brit. 

 Strom, p. 3), that an examination of the original specimen of 

 Stromatopora concentrica, Goldf., now in the museum of the 

 University of Bonn, proves conclusively that this often-quoted 

 type belongs to a totally different section of Stromatoporoids 

 from that in which the present species is to be placed I have 

 therefore been compelled to establish the new genus Actino- 

 stroma for the reception of this and of a number of related 

 types, and to give a new specific title to the form now under 

 consideration. 



Act'inostroma clathratum, Nich., grows usually in irregular 

 rounded masses, generally, if not always, with a non-epithecate 

 base. Mostly well-marked strata of growtli, or " latilaminfe," 

 are observable, and the radial pillars are " continuous " (as 

 in the genus Actinostroma as a whole), and pass from the 

 bottom to the top of each stratum, however thick. The pillars 

 are stout and rounded, often showing in cross sections (PI. VI. 

 figs. 1 and "6) traces of an axial canal. In vertical sections 

 well-marked concentric laminae are seen (PI. VI. fig. 2). 

 The pillars and laminge are about the same average distance 

 apart, viz. from |- to | millim., German specimens having these 

 structures closer than English examples f. The horizontal 

 " arms " are very regularly produced, and give rise by their 

 union to an extremely regular " hexactinellid " structure, the 

 zooidal pores being angular in shape (PI. VI. figs. 1 and 2). 



* Haviiip; had the advantage of exauiiniuo- many of Bargatzkv's! speci- 

 mens with himself, and having purchased his collection since his death, I 

 am able to speak confidently as to most of the types described in his 

 work on the Stromatoporoids of the Rhenish Devonian formation. 



t Owing to the great range of individual variation little stress can be 

 laid in most Stromatoporoids upon precise measurements, such as the 

 above. It is also noticeable that if we compare specimens of what Ave must 

 regard as the same species from distant localities (i. e. specimens from the 

 British Devonian rocks with others from the Rhenish Devonian, or speci- 

 mens from the British Silurian with examples from the same formation in 

 Sweden or Esthonia), we find them to invariably exhibit certain slight 

 but constant differences. 



