840 The American Naturalist. [September, 
The genus Conocoryphe is absent. This is specially a type of the 
Lower Paradoxides beds, and under the name of Conocoryphe trilineata 
(Atops trilineatus) is claimed as a characteristic fossil of the Olenellus 
Zone. 
The genus Mierodiscus is absent. This trilobite is especially charac- 
teristic of the Olenellus Zone, and continued to live with Paradoxides. 
The genus Olenellus is absent. Hence, although this fauna appar- 
ently holds the place where we might naturally expect to find Olenellus, 
that genus proves to be absent, or, at least, not at all characteristic ; 
and, as so many of its associate genera also are absent, we cannot regard 
this fauna as the fauna of Olenellus. 
In this fauna there is a very primitive assemblage of Brachiopods 
and at least one pelagic mollusc, having a helicoid shell and supposed 
to be free swimming Heteropod. 
The author distinguishes this fauna from that of Olenellus by two 
marked features ; it is more primitive and also more pelagic. The former 
is shown by the trilobite forms, and the latter by the following facts ; 
The absence of forms differentiated for shore-conditions ; trilobites with 
fixed outer cheeks are absent; calcareous corals and sponges are rare; 
thick shelled Brachiopods and Orthidae are rare: no Lamellibranch is 
known, but Foraminifera are common in some of the beds. (Science, 
April, 1895.) 
Formation of Oolite.—In view of Dr. Rothpletz’s recent inves- 
tigations concerning the lime-secreting fission-algae of the Great Salt 
Lake, and his own studies of the structure of the Jurassic Pisolite, Mr. 
Wethered offers the following explanation of the formation of Oolitic 
granules: 
Minute fragments of remains of calcareous organisms, such as corals, 
polyzoa, foraminifera, crinoids, ete., collected on the floor of the sea. 
These became nuclei to which the oolite-forming organisms attached 
themselves, gradually building up a crust. Sometimes this growth was 
concentric, sometimes at right-angles to the nucleus, or the two com- 
bined. When the growth was concentric, other tubules frequently 
cropped up in other directions and crossed the concentric tubules. At 
the same time, calcareous material was secreted, and the interstitial 
spaces between the tubules were filled. 
The oolite-forming organisms may be allied to the algae, or they may 
be even lower in the scale of life. Girvanella, identified by the author 
in the Jurassic Pisolite, the first type of oolite-forming organism dis- 
covered, is simply a tubule. (Quart. Journ. Geol. Soc., 1895.) 
