civlii GENERAL SUMMAEY OF SCIENTIFIC AND 



it would seem, he says, " not only that the mollusca and mollnscoida 

 (polyzoa and brachiopods) are related, but that they are connected 

 so closely that the advisability of such a division is very doubtful." 

 He does not believe that the lamellibranchs are typical moUusks, but 

 that the gasteropods should be considered so, and that the lamelli- 

 branchs are derivations from them. 



Dr. Rabl gives an account of the embryological development of 

 certain pond snails belonging to the genera Lymnmus, Physa, Planor- 

 his^ and Ancylns. These investigations are of interest from the clear- 

 ness with which the " gastrula" stage is jDresentedin Lymnmis ovattis, 

 the same phase ("invaginate gastrula") being much more obscurely 

 marked in Lymnceiis stagnalis, as observed by Ray-Lankester. It ap- 

 pears that all the fresh-water pulmonates whose development has 

 thus far been observed have the same general mode of growth. 



The mode of development of the garden snails of Europe {Helix 

 pomatia and H. nemoralis) is discussed in an elaborate manner by 

 Dr. Hermann von Jhering, so that now we have tolerably full knowl- 

 edge of the mode of growth of the land and fresh-water snails. 



M. Gerbe finds that oysters are fitted for reproduction from the 

 first year of their life. Among these precocious mothers there are 

 some whose shell, in transverse diameter, measures hardly twenty-five 

 millimeters. Hence the prosperity of the reproducing portion of a nat- 

 ural oyster-bed does not depend only on the jDresence of large oys- 

 ters. The quantity of eggs, indeed, is generally in proportion to the 

 size of the oyster. Many oysters, especially the young, propagate 

 twice in the season, under favorable conditions. The laying of eggs 

 occurs at long intervals, possibly corresponding to lunar phases. 



Within two years many important works on shells and shell-fish 

 have been published in Europe ; while in this country it would ap- 

 pear as if our conchologists were resting on their oars. The deform- 

 ities of mollusks and their shells have formed the subject of a work 

 by Clessin. He divides the subject into three categories : (1) Mon- 

 strosities, being changes in shape of considerable amount, limited to 

 the animal ; (2) modifications in the shell caused by aftections of the 

 living organs from without; and (3) anomalies in shells caused by 

 mechanical injuries, not affecting the animal. 



An elaborate memoir, by Professor Steenstrup, on the cuttle-fishes, 

 with a description, accompanied by beautiful plates, of a new form 

 (Hemisepius), appears in the Memoirs of the Royal Danish Academy. 

 This singular short cuttle-fish was discovered at Table Bay, CajDC of 

 Good Hope, 



The shells collected by Dr. Kidder, naturalist of the Transit of 

 Venus Expedition, at Kerguelen Land, have been, according to the 

 American jSfaturalist^ worked up by Mr. W. H. Dall, who describes 

 three new genera. One of these was described in England under 

 the name Eatonia; but as this name was long since preoccupied by 



