1877.] Geography and Exploration. 439 
GEOLOGY AND PALMONTOLOGY. 
Nature or THe Lecs or TRILOBITES. — Mr. C. D. Walcott has 
published a second paper in the Report of the New York State Museum, 
entitled Preliminary Notice of the Discovery of the Remains of the 
Natatory and Branchial Appendages of Trilobites. Over two hundred 
trilobites have furnished evidence of appendages, and all were found 
resting on their backs, so that Mr. Walcott concludes that they must 
have swum on their backs. (It may be noticed here that the larval 
Limulus nearly always swims on its back, as does the Phyllopod Apus.) 
He states that “ they had a double row of appendages on each side of 
the central axis. The central or axial series were either the attachments 
of swimming lobes or rudimentary ambulatory legs. The lateral series 
were branchial in their structure, the bars serving as points of attach- 
ment for their lamellæ. It is probable that they were also used in 
swimming. Many sections show appendages beneath the head, but 
nothing satisfactory can be shown from them.” He adds: “ Additional 
evidence, obtained from sections of Calamene senaria, proves that the 
central or axial appendages were articulated to the thickened arches of 
the ventral membrane, on a line with the outer edges of the alimentary 
canal. The structure of the appendages, as shown in numerous micro- 
scopic, transparent, and opaque sections, leads me to the conclusion that 
they were the support of swimming lobes. What may have been a por- 
tion of the swimming lobe has been seen in several sections near the end 
of the appendage.” These appendages terminate either in a round, 
blunt point, or else appear as if crushed. The form and outline of the 
swimming lobe could not well be preserved. Transverse sections display 
the ventral membrane between the axial appendages, the space occupied 
by the alimentary canal, and the axial and branchial appendages. The 
axial are but one third the length of the latter. The perfect state of 
preservation of the delicate branchial appendages and the ventral mem- 
brane precludes the idea of the destruction of anything of a stronger 
texture than fleshy swimming lobes attached to the axial appendages. 
„The axial appendages could not have reached to the surface upon which 
the edges of the pleure rested, which negatives the view of their being 
in any way ambulatory in case the non-presence of articulations in the 
appendages should be called in question. The axial appendages of each 
Series approximate each other near the posterior end of the hyportoma. 
What may be called oral appendages extend out between the hypor- 
toma and the dorsal shell, or else they were articulated to a membran 
Connecting the hyportoma and dorsal shell of the head. 
GEOGRAPHY AND EXPLORATION. 
Tue GEOGRAPHICAL Work or THE UNITED STATES GEOLOGICAL 
AND GEOGRAPHICAL SURVEY OF THE TERRITORIES. — Mr. A. D. Wil- 
Son, chief topographer of Hayden’s Survey, gives in the Bulletin of the 
