and inaccurate . Later the material was air dried and shaken through nested 

 screens, which facilitated drill counting and, though still laborious, proved 

 more accurate On October .16, 1953, a 20 minute run, representative of these 

 observations, was made with the suction dredge over a piece of hard bottom; 

 this was the fourth day of dredging on this particular piece of ground. During 

 the 20 minute run 6 bushels of material retained on the 1/4 x 3 inch screen con- 

 tained a total of 1, 050 drills and 45 bushels of material passing through this screen 

 contained a total of 14, 400 small drills. The conspicuously higher proportion of 

 small drills is evident and anticipated Although the conventional oyster dredge 

 does not agitate its load to the degree performed by shaker screens, the implica- 

 tion that small drills may be washed through the screen of the standard oyster 

 dredge is further strengthened particularly when the bottom is sandy and smaller 

 materials readily wash out of the dredge or when the bottom is muddy and the dredge 

 is washed vigorously to remove excess mud before being hauled aboard. 



Cole (1942) on English oyster grounds confirms the fact that much of the 

 damage done by drills passes unnoticed since it is principally spat that are drilled, 

 and a drilled spat is very rarely seen because the drilled valve generally becomes 

 detached and broken up soon after the spat gapes open. Thus the principal evidence 

 of the activity of Urosal pinx is the failure of the spatfa.U to show up the following 

 season He notes similarly that it is practically impossible to detect the damage 

 performed by freshly hatched drills among recently set spat, and this damage may 

 be very great, 



EUPLEURA CAUDATA 



Because U. cinerea occurs more abundantly and is better known than Eupleura 

 caudata the bulk of this review is concerned with Urosalpinx , However, the more 

 impoi'ant aspects of the little known biology of Eupleura may properly be stressed 

 here . 



Galtsoff et al. (1937) report that adult Eupleura average 19 to 45 mm. in 



hejght 



There is considerable interest in the possibility that Eupleura may be in- 

 (-. easing in abunda.nce , Though the trend is not always consistent and may simp'y 

 reflect a cyclical phenomenon. T. C. Nelson (1922) stated that in Little Egg Harbor, 

 New jersey. Eupleura constituted about 9.5% of the total drill population. In a 

 coant of 10, 000 drills in Delaware Bay, J. R. Nelson (1931) observed that Eu pleura 

 comprised 2% of the total population. Sizer (1936) in the same bay found that out of 

 a total of 16. 200 drills collected, 7.4% were Eupleura but that the distribution of 

 both species varied greatly in different parts of the bay. Later he captured a total 



101 



