G. GENERAL NATURAL HISTORY AND ZOOLOGY. 269 



very slender, they are one fourth of an inch apart. 4 D, 

 March, 1872, 222. 



EARLY STAGES OF THE AMERICAN LOBSTER. 



An important contribution to zoology has appeared in the 

 June number of the Journal of Science, in the form of a pa- 

 per upon the early stages of the American lobster, by Pro- 

 fessor S. I. Smith, of Yale College. It is somewhat remarka- 

 ble that the modifications which take place in the growth of 

 so prominent a crustacean as the lobster in its progress from 

 the egg to the adult have not been studied out before, in 

 view of the great abundance of the animal and the ease with 

 which it can be procured upon the coast. The research of 

 Professor Smith, however, covers nearly the entire period in 

 question, with the exception of one stage prior to that which 

 immediately represents the form of the adult. The materi- 

 als examined were obtained by him in the summer of 1871 in 

 the vicinity of Wood's Hole, on the Vineyard Sound, in con- 

 nection with the explorations of the United States Commis- 

 sioner of Fish and Fisheries. 4 D, June, 1872, 401. 



PROFESSOR GILL'S ARRANGEMENT OF MOLLUSKS. 



Professor Gill has prepared an " Arrangement of the Fam- 

 ilies of Mollusks" for the use of the Smithsonian Institution, 

 and as a guide for the arrangement of its collections, which 

 embodies the most recent results of the relations of the fam- 

 ilies among themselves, as viewed from an anatomical stand- 

 point. In an extended introduction prefacing the list of fam- 

 ilies, he has discussed the principles of classification, especial- 

 ly their application to the mollusks, and has retained the true 

 mollusca and molluscoidea in a common primary subdivision 

 of the animal kingdom. Admitting that no common charac- 

 ters have been recognized which can be used as an exclusive 

 diagnosis of the common groups, it is thought that the diffi- 

 culty of framing such a diagnosis "appears to be the result 

 of the diversity of secondary modifications and ramifications, 

 and the extreme specialization of some forms, and loss of 

 common primitive characters, rather than of the divergence 

 of the two types from a generalized protozoon, or original 

 primordial stock." But the relations of the mollusca and 

 molluscoidea, as established by such forms as Rhodosoma, 



