1895.] Geology and Paleontology. 475 
5. There is a decided parallelism between the lakes and the strike 
of the mountains, and they occupy vast valleys surrounded by high 
ground or table-land. 
6. The mountains consist chiefly of osyatalline and schistose rocks 
and gneiss. 
7. The number of the lakes in the centre of the continent is great, some 
are salt, some > brackish with sodium and magnesium salts, and some 
are fresh. 
8. Most of them have islands. 
9. Some are surrounded by markedly escarped hills, with terraces 
rising from them. Some of these terraces denote a former higher 
level. 
10. In some places the lakes are extremely deep. Notably Lake 
Nyasa shows great variation of level. 
11. The fauna shows a marked remnant: to marine forms. (Geog. 
Journ., Feb., 1895.) 
Structure of Triarthrus.—Additional discoveries relating to 
Triarthrus give rise to the following observation, by Mr. C. E. Beech- 
er, upon its general organization: 
“ The simplicity and primitiveness of the trilobite structure will 
first impress the student. The variable number of segments in the 
thorax and pygidium in the different genera shows the unstable meta- 
meric condition of the class. The head alone seems to have a perma- 
nent number of segments and appendages. . salen) Wa the 
exception of the antennules, all other paired ipada of the animal 
seem to agree in every point of structure, and vary only in the relative 
development of certain parts. The appendages of the pygidium are 
ontogenetically the youngest, and express the typical phyllopodiform 
structure. Passing anteriorly, the joints become less leaf-like, until in - 
the anterior thoracic legs they are quite slender, and the limbs re- 
semble those of schizopods. Corresponding to this, there is through 
the whole series, a gradual development of a process from the coxopo- 
dite, forming a gnathobase to the limb. On the head these serve as 
true manducatory organs. Posteriorly, they were like the basal endites 
of Apus, and enabled the trilobite to convey food along the entire 
length of the axis to the mouth.” 
In regard to the affinities of the Trilobita, and especially their rela- 
tions to Apus, Mr. Beecher points out while a general similarity of 
of the cephalic organs of Apus and Triarthrus is apparent, yet there 
are important structural features of other parts of the body in the 
