1884.] NATURAL SCIENCES OP PHILADELPHIA. 13 



except masses of dead Serpula invested with Eschara variabilis. 

 Thiere were also no echinoderms, except one, the Gaudina arenata, 

 which occui'red in some places in considerable numbers. This, 

 it was believed, is the first time the animal has been observed on 

 the coast of New Jersey. The specimens presented were collected 

 by Mr. Ford. They usually range from three to four or five 

 inches in length ; but several were upwards of six inches, and 

 over an inch at the thicker portion of the body. 



It is an interesting question as to what becomes of the vast 

 quantities of Macira and other shells incessantly cast on shore. 

 Storms annuall}^ oblige the ocean to contribute from its inex- 

 haustible stores, multitudes of mollusks and other animals to the 

 sandy beach. By exposure to the influence of the weather, the 

 air, the sun, the rain, frosts and other violence, the calcareous 

 shells are broken and decomposed, and in a comparativel}^ few 

 years entirely disappear. Carbonic acid, of the rain-water, must 

 be a potent agent in their ultimate soliition as it percolates 

 through the sands. While the beach receives its constant sup- 

 plies of shells, no trace of these is to be found in the sands 

 immediately back of the shore ; which sands in former times 

 received the same incessant contributions. For similar reasons, 

 no doubt, calcareous fossils are comparatively rare in sandstones, 

 though in many cases their impressions are well preserved. 



Flora of North America. — At the meeting of the Botanical 

 Section of the Academy, held on January 14, Dr. Asa Gray 

 spoke of the progress of the forthcoming portion of the Synop- 

 tical Flora of North America, and of the occasions which had led 

 to the publication of the middle portions in advance of the earlier. 

 It had seemed important now to secure the results of the many 

 years of study which he had given to the large and difficult order 

 of Compositae, which will form the bulk of the forthcoming part. 

 He spoke of the perplexities attendant upon the accurate defini- 

 tion of generic divisions in this order, and especially of properly 

 discriminating the species of such genera as Aster and Solidogo. 

 He had no idea that he had really solved the difficulties of this 

 kind, or that any one would entirely solve them; but he had done 

 his best. He could himself name the species of Solidago^ and he 

 could name a good many Asters ; but he doubted whether he 

 had enabled other botanists to name them. Being asked whether 

 his views respecting the limitation of species had not under- 

 gone some change, in the direction of admitting more species now 

 than formerly, he admitted that this was probably the case. He 

 still held to what might be termed the Linnsean conception ot 

 species, that they were to be taken in a broad sense and expected 

 to comprise various forms, which might or might not be classi- 

 fied into varieties. But whereas, in his younger days, species 

 were thought to be independent creations, and the real diff'erences. 



