4 BRITISH STROMATOPOROIDS. 



form of a hemispherical mass, composed of concentrically disposed strata of 

 considerable thickness (" latilamina? "), its texture being so dense as to exhibit the 

 minute structure but imperfectly under the lens. 1 Examined microscopically, the 

 skeleton is seen not to be composed of a continuously reticulated fibre, but to be 

 built up of definite " radial pillars," which are united at regular intervals by 

 radiating horizontal connecting-processes or " arms," thus constituting a series of 

 "concentric laminse." It has, therefore, the so-called " hexactinellid structure," 

 which is characteristic of all those Stromatoporoids which were formerly referred 

 to the genus Stromatopora, and for which I shall now propose the generic title of 

 Actinostroma. Specifically, it is identical with, or very closely allied to, the form 

 which Bargatzky has erroneously identified (' Stromatoporen des rheinischen 

 Devons,' p. 56) with Stromatopora astroites, Rosen. 



(2) Tragos capitatum, Goldf. (' Petref . Germ.,' p. 13, Taf. v, fig. 6). This 

 was originally described by Goldfuss as a distinct species, but was subsequently 

 (in a later portion of the ' Petrefacta ') referred by him to his Stromatopora 

 polymorplia. The original specimen shows that this form possesses the continu- 

 ously reticulated skeleton and the minutely porous skeleton-fibre which charac- 

 terise the group of the Stromatoporidai proper ; and it must be referred either to 

 Stromatopora, Goldf., itself or to some allied genus. Thin sections of the original 

 specimen do not exist, but I have collected from the Devonian Limestones of the 

 Paffrath district a number of examples of apparently the same species, and a 

 minute examination of these has led me to think that the species should probably 

 be referred to the genus Idiostroma, Winchell. In any case the species is one 

 quite distinct from the true Stromatopora concentrica, Goldf. 



(3) Geriopora verrucosa, Goldf. (' Petref. Germ.,' p. 33, Taf. x, fig. 6). 

 In the later portion of his work Goldfuss referred this form also to Stromatopora 

 polymorplia. A superficial examination of the original specimen shows that this 

 type is really referable to what I shall now term Actinostroma (i. e. to what has 

 previously been regarded as Stromatopora proper), the skeleton being made up of 

 "radial pillars" and horizontal connecting-processes. It is a good species, and 

 is common at certain localities in the Rhenish Devonians (e. g. at Biichel). It will 

 stand as Actinostroma verrucosum, Goldf. sp. 



(4) Stromatopora polymorplia, Goldf. Under this name Goldfuss included a 

 number of quite distinct forms which are at present only partially known. The 

 forms in question are as follows : 



(a) A group of encrusting forms (' Petref. Germ.,' Taf. lxiv, figs. 8 a, 8 c, 8 d), 

 which seem to be referable to what I shall subsequently define as Stromatoporella. 

 They are common in the Devonian Limestone at Biichel, and we may follow 



1 Precisely similar specimens are abundant at Gerolstein in association with the true S. concen- 

 trica, Goldf., the latter being, however, much less common. 



