try for sixty miles and more, parallel to the mountain axis. Most 



the summits of these rock crests, and almost all the more inaccessi- 

 ble and remote points of the hills. They were often found standing 

 on the summits of ledges of from five to twelve feet in width, with 

 precipices of several hundred feet in depth on one or both sides ; 

 or occupying ledges on the sides of precipices forming the walls 

 of canons, in positions only accessible by perilous climbing. 

 These localities are often remote from water, in some cases more 

 than twenty miles. 



The party collected and brought within reach of transportation 

 about a ton of fossil remains. They crossed directly from the 

 Rio Puerco to Conejos over the San Juan Mountains by a pass 

 some twenty miles in length, where they were overtaken by a 

 severe snowstorm. They returned to Pueblo on the 11th of No- 

 vember. 



REVIEWS AND BOOK NOTICES. 



Embryology of the Ctenophokje. 1 — The development of 

 certain jelly fishes (Ctenophorse) belonging to the genera Idyia 

 and Pleurobrachia has been elaborated in this memoir with great 

 care and beauty of illustration by Mr. A. Agassiz. He gives a 

 connected account of their history from the earliest stages in the 

 egg until all the features of the adult appear. While the mode of 

 segmentation of the yolk is extraordinary, the embryo attains the 

 adult form without any metamorphosis, the changes being very 

 gradual. Mr. Agassiz's observations, with the preceding ones of 

 Midler, Gegenbaur, Kowalevsky and Fol, give us a tolerably com- 

 plete view of the mode of development of this order of jelly 

 fishes. These Ctenophorse on our coast spawn late in the summer 

 and fall. The young brood developed in the autumn comes to the 

 surface the following spring nearly full-grown, to lay their eggs 

 late in the summer. The autumn brood most probably passes the 



for the young to attain their maturity. The memoir closes with 



