394 Bibliographical Notices. 



sites and Heliolites ; but from the quadripartite character of the 

 septa, Prof. Safford regarded the genus as referable to the Puigosa. 



The group Thecidae includes but one genus, Thecia, restricted to 

 the Silurian rocks, the typical species of which, T. Swinclerniana, 

 Goldf., the author has submitted to a careful macroscopic and micro- 

 scopic investigation, from which it seems to form, in some respects, 

 a link between the Perforate Corals and the Alcyonarian family of 

 the Helioporidae. For the structure and relations of the Helio- 

 poridae we are indebted to the researches of Mr. Moseley (Phil. 

 Trans, vol. clxvi. pt. 1, p. 91), which prove that Heliopora and its 

 ancient allies are truly Alcyonarians. Most of the genera are 

 Palaeozoic ; one (Polytremacis) is Secondary ; and Heliopora is both 

 Cretaceous and Pecent. 



The next group, the Chaetetidae, Dr. Nicholson considers to be 

 made up of very heterogeneous materials, which must ultimately 

 be disintegrated. The chief member (Chcetetes radians) and its 

 allies are in some respects similar to the Favositidae, " except 

 that 'mural pores' in the walls are wanting, while there are (in 

 reality) no traces of septa, and the walls of the corallites are com- 

 pletely amalgamated." Although these forms are far removed from 

 the Favositidae, he is satisfied that they are genuine Actinozoa, and 

 seem to have more affinities with the Alcyonaria. 



The group Monticuliporidae, founded on the genus Monticulipora, 

 D'Orb., and originally considered to be a Bryozoan, includes nume- 

 rous forms whose position is uncertain, and which " constitute 

 perhaps the most difficult and intricate assemblage of Palaeozoic 

 fossils with which the zoophytologist is called to deal " (p. 270). 



Although giving the results of his investigations in considerable 

 detail (pp. 270-330) as to the internal structure of the corals 

 usually referred to Monticulipora and allied types, Dr. Nicholson 

 proposes to publish hereafter an entirely separate memoir on the 

 group. He considers, however, that although strong evidence has 

 been brought forward to prove these forms to be Polyzoa, yet, from 

 their general structural character and resemblance to Ccelenterate 

 types, the majority will prove to belong to the Actinozoa. 



The last family, Labechidae, comprises the anomalous genus Lahe- 

 chia, originally placed by M. -Edwards and Haime among the Chaete- 

 tidae, and considered by Dr. Lindstrom truly a Hydrozoon allied 

 to Hydractinia. The peculiarities in its structure, however, are so 

 numerous, and the apparent total absence of superficial openings of 

 any kind is so puzzling, that Dr. Nicholson does not at present see 

 how it can be placed among either the Hydrozoa or the Actinozoa. 



We have attempted but a brief and imperfect sketch of the chief 

 views of Dr. Nicholson on the twelve subdivisions of the Tabulata, 

 which the reader will find given in detail in the separate chapters 

 treating of each special group. 



That some of the conclusions arrived at will be generally accepted 

 the author does not expect ; but while acknowledging the assistance 

 he has derived from the labours of previous observers, it is fair to 

 state that most of the facts recorded in the volume have been veri- 



