34 The Molluscan Family Plaiwrbidae 



On June 25, 1933, the same three snails showed some growth: 



1 specimen 5.5 mm. in diameter with 3% whorls. 



1 specimen 6.5 mm. in diameter with 3^/i> whorls. 



1 specimen 6.5 mm. in diameter with S^/v; whorls. 

 On August 6, 1933, but two snails remained alive. These measured: 



1 specimen 6 mm. in diameter with 3^2 whorls. 



1 specimen 6.8 mm. in diameter with 3^-2 whoi-ls. 

 These 3^oung snails li^•ed 570 to 580 days after hatching and increased in diameter 

 from 1.1 mm. to 6.8 mm. and in number of whorls from one to three and a half. An 

 adult nor male measures about 20 mm. in diameter and has five whorls, so that the 

 young snails were about one-thiixl grown after a development period of one year and 

 seven months. If this growth is normal, it must require three or four years for this 

 race to attain maturity, unless there is considerable acceleration in growth during the 

 second or third years. The tem])erature in which the young snails were reared was 

 ordinary room heat between 70 and 75 degrees F. This temperature reached 90 degrees 

 or more in the hot .summer months. The matter of food is also important since only 

 filamentous algae were jilaccd in the aquaria, the snails feeding mostly, howe\er, on 

 the green algal deposit which formed on the glass sides of the aquaria. 



[4} HeXisoma duryi ^udiscus Pilsbry 



Si>ccimens of this race of duryi were received from Mr. T. Van Hyning, of the 

 Florida State Museum, collected at Silver Springs, Marion County. They were re- 

 ceived at the laboratory on October 2, 1931. On December 13 an egg capsule was laid 

 measuring 2 by 2.5 mm. in area with five eggs. On February 6, 1932, another capsule 

 was laid measuring 2 by 4 nmi. with nine eggs, and on February 12 a capsule with 

 seven eggs. On February 10 a large capsule measuring 5 by 4 mm. was deposited 

 containing twelve eggs. One capsule (Feb. 10) developed to the gastrula stage and 

 then ceased growth. Another was disintegrated and the space was filled by Protozoa. 

 A third capsule (Feb. 12) completed its development, all of the embryos being 

 hatched. 



A single adult cudisciLS was left in the aquarium and on June 11, 119 days after 

 the laying of the last egg capsules, egg laying began again with the deposition of a 

 capsule measuring 4 b.v 3.5 mm. and containing two eggs, each egg 1 mm. in diameter. 

 On Jime 13 the eggs had reached the gastrula stage. From June 14 to June 26 the eggs 

 remained in the same stage and at the last date the eggs appeared to disintegrate. 



[5] HeXisotna tenue. cali^oyr\,i&ns& F. C. Baker 



Specimens of this race were recei\ed from Dr. S. S. Berry, collected from Prospect 

 Park, near Redlands, San Bernardino Mts., California. They were placed in an aquari- 

 um on February 12, 1932, and laid nine egg capsules on the next day. The nine 

 capsules contained 199 eggs as noted below: 



No. 1. 4 by 4 mm. in diameter containing 15 eggs. 



2. 5 by 3.5 mm. in diameter containing 18 eggs. 



3. 4 by 7 mm. in diameter containing 21 eggs. 



4. 6 by 3.5 mm. in diameter containing 28 eggs. 



5. 4 by 5 nun. in diameter containing 15 eggs. 



6. 4 by 4 mm. in diameter containing 11 eggs. 



7. 4 by 7.5 mm. in diameter containing 27 eggs. 



8. 4.5 by 7 mm. in diameter containing 26 eggs. 



9. 5 by 8 mm. in diameter containing 38 eggs. 



Development was fairl.v regular and occupied fifteen days, from February 13 until 

 February 28. A typical development is indicated below: 

 Feb. 14. Segmentation begun. Feb. 23. Embryos with shell forming. 



15. Segmentation ancl gastrula stages. 24. Embryos with shell ^3 filling 



16. Gastrula and trochophore stages. membrane. 



17. Trochophore and preveliger 25. Embryos with shell filling % 



stages. and y^ of membrane. 



18. Early veliger stages. 26. Embiyos with shell filling % of 



19. Veliger stages. membrane. 



20. Early embryo stages. 27. Embiyos with shell completely 



21. Early embryo stages. filling membrane. 



22. Embryos with shell forming. 28. All hatched. 



