(Review of (Rece^it Geological Literature. 255 
REVIEW OF RECENT GEOLOGICAL LITERATURE. 
0« ike structure and affinities of the genus Parkeria Carp. By H. Ali.eyne 
Nicholson (Ann. and Mag. of Nat. Hist., Jan., 1S88). This paper, in com- 
mon with nearly all of Dr. Nicholson's works, is evidently the result of 
painstaking and sytematic inquiry, being a careful record of observations 
made during the progress of a minute investigation into the structure of 
the peculiar genus Parkeria. His observations are founded upon an 
abundance of good material and extensive series of thin sections mainly 
prepared by himself. 
The author begins his paper with a condensed history of the genus. 
From this we learn that Parkeria was originally described by Dr. W. B. 
Carpenter in 1870 (Phil. Trans., vol. clix, p. 721), and that the genus was 
regarded by this eminent authority as belonging to the arenaceous fora- 
minifera. In 1876 and 1877 the structure of the genus was investigated 
by Mr. Carter, who came to the conclusion that the skeleton was aot 
arenaceous and that the genus should be referred to the Hydractiniidse. 
Mr. Carter's views have, in the main, been accepted by subsequent 
writers, such as Steinmann and Zittel, and are now concurred in by Dr. 
Nicholson. 
The ordinary form of Parkeria presents itself in the shape of spherical 
bodies, varying in diameter from less than half an inch to about two 
inches. Most of the specimens must have been entirely free in the adult 
condition, but some at any rate, commenced growth upon some foreign 
body. The surface of unworn examples generally exhibits rounded or 
elongated elevations; in other cases it may present an alveolar or honey- 
combed aspect. Rough fractures show that the skeleton is composed of 
numerous cylindrical columns ("radial pillars") which traverse the fossil 
in a radial manner from the center to its circumference, and are united 
at more or less regular intervals by imperfect concentric layers, separ- 
ated from one another by concentrically arranged interspaces ("chamber- 
lets"). These interspaces, or rather each successive tier of them, repre- 
sents what was at one time the surface of the organism. 
As regards the chemical constitution of the fossil skeleton, great differ- 
ences are noticed in large series of specimens, in some it being composed 
of carbonate of lime, with the chambers of the fossil occupied by calcite 
or by an infilling of the matrix in which the specimen was originally im- 
bedded. In the majority of cases the skeleton is more or less extensively 
composed of phosphate of lime with the chambers occupied, throughout 
or in part, by phosphatic infilling, while in a third group of specimens in 
which the skeleton is also largely composed of phosphate of lime, the 
central portion or the whole of the fossil has its chambers empty. 
The question, what was the original composition of the skeleton Par- 
keria is carefully considered. Carpenter's view, that it was composed 
