Reviews — Prof. Dr. Nicholson — British Stromatoporoids. 127 



not so striking a resemblance is also seen when the comparison is 

 made with the Hydractinia circnmvestiens from the Red Crag of Suf- 

 folk, which possesses a calcareous ccenosteum. The typical Stromato- 

 poraa, on the other hand, are more closely comparable with the cceno- 

 steum of Millepora. But as both the groups of Stromatoporoids are 

 linked together by intermediate forms, and thus constitute a natural 

 series, it is better to retain these fossils as a peculiar division of the 

 Hydrozoa 



(IV.) Sketch Classification. — This is to be accepted as largely tenta- 

 tive, as many of the types have not yet been properly examined. 

 The following tabular view is given by the author. 



Order. — Stromatoporoidea, Nich. and Murie. 

 Section A. (" Hydractinioid " Group). 

 Fam. 1. Actinostromidaa, Nich. 

 Genera — Actinostroma, Nich. ; Clathrodichyon, Nich. and Murie ; 

 Stylodictyon, Nich. and Murie (?). 



Fam. 2. Labechiidas, Nich. 

 Genera — Labechia, E. & H. ; Bosenella, Nich. ; Beatricea, Bill. (?) ; 

 Dictyostroma, Nich. (?). 



Section B. ("Milleporoid " Group). 

 Fam. 3. Stromatoporidas, Nich. 

 Genera — Stromatapora, Goldf. ; Stromatoporella, Nich. ; Parallelo- 

 pora, Barg. (sub-genus?); Syringostroma, Nich. (sub-genus?). 



Fam. 4. Idiostromidae, Nich. 



Genera — Idiostroma, Winch. ; Hermato stroma, Nich. ; Ampliipora, 

 Schulz ; Stachyodes, Barg. 



(V.) Families and Genera of the Stromatoporoids. — Detailed descrip- 

 tions are given of the characters of the various members of the 

 group, to which space prevents further reference, but the inclusion 

 of the peculiar forms known as Beatricea, Bill., as a genus of 

 Stromatoporoids, calls for some notice. These fossils are cylindrical 

 or angulated rods or stems, often of considerable size, some reaching 

 10 feet in length by one foot in thickness. They possess a central, 

 relatively large, axial canal, without definite walls, and divided by 

 superposed, curved, tabula?. Between the central canal and the 

 exterior of the fossil, the skeleton consists of concentric layers of 

 vesicular tissue. The position of these fossils has long been regarded 

 as uncertain, and one observer, Prof. Hyatt, who formerly referred 

 the genus to the Cephalopoda, now degrades it to the Foraminifera. 

 The general opinion has been in favour of its alliance to the 

 Cystiphylloid Corals. The fossils are generally very imperfectly 

 preserved, but Prof. Nicholson has detected, in some specimens, 

 structures radiating from the central canal towards the circumference, 

 which he regards as " radial pillars " essentially similar to those of 

 the genus Labechia. The axial tabulate tube is regarded as parallel 

 with the tubes in Idiostroma, Stachyodes, and Ampliipora. But the 

 axial tubes in these forms are so much smaller than those of Beatricea, 



