MINITTE STEXJCTUEE OF STEOMATOPOEA AND ITS ALLIES. 229 



ally porous. Even the huge lamellae of Pacliystroma, each of which 

 probably represents several amalgamated lamellas with their in- 

 tervening interspaces in the ordinary Stromatoporoids, cannot be 

 properly said to be " labyrinthic." 



(<?) The "radial" pillars of Parkeria are perforated by large 

 canals. This is not the case, as a rule at any rate, with the Stro- 

 matoporoids, whilst there are forms amongst the latter in which 

 the radial pillars are entirely wanting. 



{d~) In their general form and habit, the Stromatoporoids diifer 

 widely from Parkeria^ the latter being free, whilst the former were 

 attached to foreign bodies and sometimes incrusting or parasitic. 



{e) Nothing comparable with the nucleus of Parkeria^ can be 

 detected in any Stromatoporoid. 



3. To Sponges. — According to Von Eosen the fossil form Spar- 

 sispongia, D'Orb., is really referable to the Stromatoporoids. If 

 such is proved to be the case, it would seem not unlikely that the 

 secondary genus Stellispongia, D'Orb., may really belong to the 

 same group. But as we have had no opportunity of examining 

 specimens of either of the above minutely and critically, for the 

 time being we must leave the question open. The same may be 

 said of certain other forms — to wit, Spongia stellata, Lams., and 

 specimens designated in our museums Sphcerospongia. 



It certainly is to the Sponges, more frequently than to any 

 other group, that the Stromatoporoids have been referred by 

 previous observers, including one of the present writers ; and 

 they have been placed, collectively or as regards individual form, 

 in the groups of the Horny, the Siliceous, and the Calcareous 

 sponges. On the whole subject of the relationship between the 

 Stromatoporoids and the Sponges, we shall content ourselves 

 with adducing the following considerations : — 



First, the reference of the Stromatoporoids to the Horny 

 Sponges, chiefly supported by the authority of Von Eosen, we 

 believe to be entirely inadmissible ; and, without entering into 

 the question in detail, we may simply state that this conclusion 

 was essentially based on the assumed fact that the Siliceous 

 Sponges of the Chalk, since undoubtedly proved to possess a 



* Our friend Dr. John Millar has enabled us to examine a series of most ex- 

 cellent specimens illustrating the structure of Loftu&ia and Parkeria. Two 

 distinctive kinds of Parkeria, both in considerable abundance, hare been got by 

 him from the Cambridge beds. He ia inclined to regard Parkeria as evincing 

 affinities with the Polyzoa rather than strictly with the Foraminifera ; but as 

 his researches are still in progress we must defer further notice. 



