236 HYDROZOA. 



massive skeleton is formed of a series of thick concentric strata 

 ("latilaminae"), each of which is made up of subordinate concentric 

 " laminae." The type of this genus is the Stromatopora concentrica 

 of Goldfuss, a comparatively rare species in the Middle Devonian 

 of Germany and Britain. Upon this species Goldfuss founded the 

 genus Stromatopora, but the name has been erroneously given to 

 various Stromatoporoids of quite different affinities. Other species 

 of Stromatopora are found in the Silurian and Devonian rocks ; and 

 the allied genus Stromatoporella appears to be principally if not 

 wholly Devonian. 



Lastly, there is a group of Stromatoporoids, represented by genera 

 such as Idiostroma and Amphipora, in which the skeletal tissue re- 

 sembles that of Stromatopora in its reticulated character, but the 

 ccenosteum is cylindrical and often branched, and is provided inter- 

 nally with a comparatively large axial tube intersected by cross 

 partitions or "tabulae." The genera above-mentioned are both 

 Devonian, and the sole known species of Amphipora (viz., A. 

 rainosa) is an abundant and characteristic fossil in the Middle 

 Devonian of Germany and Britain, its slender cylindrical stems 

 occurring in great abundance in particular beds in this formation. 



Before leaving the subject of the Stromatoporoids, allusion may be 

 made to the fossils which have been described under the name of Canno- 

 pora. The fossils in question resemble the ordinary Stromatoporoids, 

 and indeed are only Stromatoporoids of various species, with the pecu- 

 liarity that the general tissue of the ccenosteum is traversed by a number 

 of comparatively large, thick-walled vertical tubes, which open on the 

 surface by definite round apertures. These tubes often spring at the 

 base from horizontal stolons, and are usually connected here and there 

 by lateral tubes of a similar structure to themselves ; they usually, if not 

 always, have funnel-shaped, or sometimes horizontal, internal calcareous 

 partitions or " tabulae," and they occasionally possess rows of short 

 "septal spines." It has been shown that the same species of Stromato- 

 poroid may occur with or without these peculiar " Caunopora-tubes," and 

 there exists further an obvious likeness between these tubes and the 

 corallites of such corals as Aalopora and Syri?igopora. Upon the whole, 

 therefore, it may be regarded as probable, if not absolutely certain, that 

 the fossils usually grouped together under the name of " Can?wpora " are 

 Stromatoporoids which in course of growth have enveloped a colony of 

 some such coral as an Aidopora or Syri?igopora, the latter not being 

 thereby killed, but continuing to grow and flourish as a " commensal " 

 within the tissues of the Stromatoporoid. 



As regards the zoological affinities of the Stromatoporoids, their 

 general structure seems to render it certain that they are referable to 

 the Hydrozoa, of which they must be considered to form a special and 

 now unrepresented group. Certain forms (such as Actinostroma and 

 Labechia) show a decided relationship with the recent Hy dr actinia ; 

 while others (such as Stro?natopora itself) are more closely connected 



