376 



ten, largest) of the males, in the next three columns the dimen- 

 sions of the females (average of fifteen). In the last two columns 

 the measurements of a male and a female from California. 



Total length of body 545 600 640 645 670 705 690 770 



L. of notogastral plate 470 485 525 520 540 570 555 635 



Breadth of same 375 410 440 425 460 495 475 565 



Interlamellar bristle span 75 80 85 75 90 100 100 110 



L. of vent, plate (mid.) 400 445 470 485 500 535 520 600 



Camerostome to gen. apert 100 102 105 100 103 105 100 110 



L. of genital aperture 70 73 80 80 83 90 80 93 



Breadth of same 78 82 85 85 93 100 85 110 



Gen. apert. to anal apert 115 131 150 145 161 175 170 220 



L. of anal aperture 100 109 115 110 119 125 125 135 



Breadth of same 105 114 120 125 130 145 150 



It should be noted that length of ventral plate is actual length 

 on median line and not measured to overlapping edge of noto- 

 gastral plate. All these measurements are as made in mounted 

 specimens by micrometer eye piece and do not take curvature into 

 consideration. Apparent length of cephaloprothorax varies with 

 angle at which the body is tilted. The same is true of the abdo- 

 men. 



The majority of specimens measured were from one locality 

 (near Stevenson, Conn.) and these specimens cover the range of 

 size here recorded. Specimens from Sea Cliff, Long Island, N. Y., 

 and from Hamden, Conn., are included by this range. Specimens 

 from Maine average larger but do not exceed the Connecticut 

 specimens. The much shattered Georgia material includes fe- 

 males with genital covers 94 micra long. Thus there seems to 

 be a rather definite size limit along the eastern states especially 

 the northeastern. Most striking however, is that there is a dif- 

 ference of a hundred micra between the largest Connecticut and 

 the smallest European specimens. 



From the table it will be evident (1) that breadth of genital and 

 of anal apertures as well as distance between them is quite vari- 

 able, (2) that there is marked sexual dimensurism, (3) that 

 breadth of genital aperture and interlamellar bristle span are 

 practical^ equal, (4) that the ventral plate apertures are broader 

 than long, (5) that the anal aperture of the females seems rela- 

 tively broader than that of the males. 



Aherations. — One specimen has three bristles on one anal cover 



