882 American Work on Recent Mollusca in 1881. [November, 



failed entirely on account of their minute size, and in spite of the 

 sanguine hopes expressed by Messrs. Ryder and Brooks, there 

 does not appear to us to be any reasonable prospect of success in 

 the project except at an expense which would in practice prove 

 prohibitory. Mr. Ryder also gives figures of young oysters of 

 known age, which illustrated the greater energy and extent of 

 growth in the American (0. virginiana) as compared with the 

 European (0. ediilis) oyster. 



The second paper was noticed in this record for 1880, and in 

 view of possible doubts as to the species of oyster observed upon, 

 it is desirable that the experiment should be repeated with un- 

 doubted 0. ednlis. It is really surprising that, with their facili- 

 ties, the European naturalists have hitherto failed to give us a 

 comprehensive monograph of one of the commonest and per- 

 haps the best known moilusk in the world. 



The name " clam " in America is commonly applied to any 

 bivalves not "mussels" or "cockles." In New England the clam 

 is Mya arenaria, in New York it is Venus mercenaria. In the for- 

 mer region the Venus is known as the " hard " or " round " clam ; 

 in the latter the Mya is called " soft shell " or " longneck " clam. 

 The name " mananose " -is a southern appellation for the Mya, 

 perhaps of Indian origin. Mr. Ryder's observations on the early 

 stages of Mya are full of interest. This moilusk spawns in Sep- 

 tember and October during a period of about forty days. It is 

 dioecious. The changes in the egg succeed each other with con- 

 siderable rapidity, and as in the development of the oyster there 

 are marked periods of active change of form which alternate with 

 periods of repose. Bilateral symmetry is marked. The eggs are 

 about gfa inch in diameter. Their segmentation^ far as followed, 

 resembled that of Anodonta, and the gastrula stage is formed in 

 the same way as in the oyster. 



A portion of a letter from Mr. Henry Hemphill, of California, 

 relating to variations due to station, in the genus Acmaea appears 

 in Proc. Acad. Nat. Sci. Phil., 1881, pp. 87-8, in which the iden- 

 tity of the so-called Nacella instabilis Gld., with Acmcea pelta 

 Esch., is claimed. The recorder showed long since that the 

 " Nacellae" of Carpenter's lists were all referable to Acmaea ex- 

 cept one, which is an Anisomyon belonging to the Siphonarudae. 

 If an examination of the soft parts confirms Mr. Hemphill s 

 views, it will be a very striking illustration of the influence of 

 food and station on external characters. 



