of tanks. Drills put in the bottom of a vertical 

 glass tube about 1 inch in diameter and 6 to 8 

 feet tall, filled with sea water, will climb to the top 

 of the tube and remain there. Negative geotaxis 

 is pronounced, particularly during the reproduc- 

 tive period. At this time drills climb on any 

 objects above the bottom level and ascend rocks 

 and various underwater structm'es to lay theu- 

 eggs, which are deposited in tough, leathery cap- 

 sules (fig. 389, 3). The egg-laying period depends 

 on geographical location and local conditions. 

 Summarizing the data from various sources, 

 Carriker (1955) estimates that the number of 

 egg cases deposited by one drill per season ranges 

 from (in an imnuiture female) to 90 for older 

 females. In Woods Hole harbor, the breeding 

 season lasts from the end of June to the middle 

 of August. The number of egg cases deposited 

 by a single female kept in laboratory tanks 

 varied from five to nine; the average nmnber of 

 eggs in each case was nine. The number of eggs 

 per egg case varied in different localities from 

 eastern Canada to Chesapeake Bay from to 

 22 and from 1 to 29 in British oyster beds. (Cole, 

 1942). 



A second species of drill, Eirpkura caudafa 

 (Say), (fig. 390), is found in the same waters as 

 Urosalpinx but is usually less abundant. Various 



observers estimate that in different locations it 

 comprises from 2 to 29 percent of the total diill 

 population (Carriker, 1955). The behavior of 

 Eupleura is similar to that of Urosalpinx. Its 

 food habits have not been studied, but occasional 

 observations in the laboratory indicate they are 

 probably not different from those of Urosalpinx. 



In the York River, Va., where the growth and 

 reproduction of Eupleura were studied by Mac- 

 Kenzie (1961), the snail becomes active as the 

 temperatm-e rises over 10° C. Spawning begins 

 late in May at 18° to 20° C, reaches a peak in 

 June and early July at 21° to 26° C, and ends in 

 early August. Mature females (kept in cages) 

 deposit an average of 55 cases, each containing 

 an average of 14 eggs. In the absence of mortal- 

 ity, each female Eupleura may produce over 700 

 young di'ills each season. The leathery egg 

 capsules are vase-shaped with two distal pro- 

 jections (fig. 390, 3) and are easy to distinguish 

 from the egg cases of Urosalpinx (fig. 389, 3). 



Conchs of the genus Thais occur on both the 

 Atlantic and the Pacific coasts. The snails have 

 strong polymorphic tendencies and form local 

 races which greatly complicate the taxonomy of 

 the species. A review of the speciation problem 

 of T. lamellosa Gmelin made by Kincaid (1957) 



I. 











432 



Centimeters Centimeter 



Figure 390. — Eupleura caudala (Say) from 1 — apertural side; 2 — from abapertural side, 3 — egg cases. 



FISH AND WILDLIFE SERVICE 



