16 



THE NAUTILUS. 



being due to the eroded umbones, but with young specimens 

 showing umbonal sculpture, it was an easy matter. Simpson 

 says in his Descriptive Catalogue for both species, that the um- 

 bonal sculpture was not seen; hence no description. This 

 museum has numerous specimens of young and adult of both 

 species recently collected, and the young show the umbonal 

 sculpture of both species to be composed of about four coarse 

 ridges; in minor they are circular and in villosa V-shaped looped. 



Mr. Frierson, in a letter of November 27, '16, writes that he 

 has discovered how to differentiate the adults of these two 

 species. He calls attention to an additional small muscle scar 

 (cicatricula?) at the upper end of the anterior muscle scar 

 (cicatrix) in minor. 



I have just found time to go over the specimens in this 

 museum and open them up, and separate them according to 

 Mr. Frierson' s discovery, and I am now prepared to give some 

 additional information. In the majority of specimens a glass 

 is required to see the small scar referred to, and then in the 

 majority of specimens the small scar, instead of being separate, 

 is but an extension of the larger one, which makes it still 

 harder to determine. Simpson says, of minor, 1 i anterior scars 

 deep," and of villosa u muscle scars scarcely impressed." In 

 opening a shell, the deep scar in minor is at once noticeable from 

 the shallow one of villosa. Minor is a heavier, wider, and shorter 

 shell than villosa, and the anterior distance from the umbo is 

 shorter in minor. 



Florida State Museum. 



NOTES ON REPRODUCTION AND GROWTH IN CERTAIN VIVIPAROUS 

 MUSSELS OF THE FAMILY SPHAERIIDAE. 



BY RALPH J. GILM0RE. 



The present study was undertaken in an effort to determine 

 the nature of the reproductive process in certain common forms 

 of the family Sphaeriidae. For a long time incubation of the 

 young has been known to occur in European forms, but no in- 

 vestigation has been made of related forms from America. 



