65 



of which it differs in the flatness of its whorls, in its aperture, 

 which is proportionally much longer and narrower, and in being 

 only about half their size. It is much like large specimens of 

 Physa hypnorum reversed. 



Prof. Agassiz read a paper on the necessity of a thorough 

 revision of the system of classification in Zoology now in 

 use. He gave a sketch of Cuvier's system, and showed its 

 many deficiencies in the present advanced stage of science. 

 He thought that a more perfect system was called for, based 

 upon the embryonic development of animals, and the order 

 of their appearance at the various geological epochs. His 

 views were illustrated by many interesting facts. Dr. Gould 

 followed with some interesting observations in confirmation 

 of Prof. A's. views, drawn from his study of the Mollusca. 

 He had noticed among them a structural agreement, accord- 

 ing to their position in the scale, with the order of geologi- 

 cal succession. Points to which he alluded in illustration 

 were the degree of development of parts, as that of the 

 head, for instance ; the development of distinct organs, as 

 of the eyes ; and the shape of the shell. 



Mr. Desor gave an account of his recent zoological inves- 

 tigations among the shoals of Nantucket, whilst on board 

 the surveying steamer Bibb ; Capt. Davis having afforded 

 him every opportunity for dredging in depths varying from 

 three to twenty-five fathoms. 



Among the radiated animals which thus came under his 

 examination were the following: 



HYDROIDIAN POLYPS. 



1. Plum ARIA A RBOREA, Desor. Polypidom arbuscular, irregu- 

 larly branched ; branches long and pinnate, the pinnae leaning 

 to one side. Cells pyriform, with a plain margin, very close 

 together, on the internal side of the branches. From 4 to 6 

 inches high. Dredged on the Shoals of Nantucket, ten miles 

 east of Sancati Head, from a depth of fourteen fathoms. 



2. Sertularta filicula, Ellis. From 2 to 3 inches high. 



PROCEEDINGS B. S, N. H. 5 NOV. 1848. 



