OCR Text |
Show 254 MR. R. COLLETT ON BAL^LNOPTERA BOREALIS. [Feb. 2, individuals 320, in others as many as 340. No. 2 for instance had on its right side only 318, on its left 328. The number appears to be rarely the same in the two jaws of the same individual. The front plates were small, almost rudimentary, and formed double rows ; these were difficult to count. The greatest length was attained at the commencement of the latter third of the series, where as a rule they measured 550 to 600 millim.1 From these measurements it appears that the length and number of the plates are not constantly greater in the right than in the left jaw, also that there is no constant difference between the plates in the two sexes. The hair-like bristles in which each plate terminates, and which form the most effective part of the straining-apparatus, are in this species unusually fine, somewhat resembling silky wool, and white 1 I give here the measurements of the baleen-plates of 4 examples, viz. of specimens Nos. 1, 3, and 5, and those of a fourth individual, the jaw of which lay on the beach. They are reckoned from behind forwards, so that No. 50 lies near the angle of the mouth, No. 250 nearest the symphysis of the jaw. They are measured from their base (in the freshly killed specimen) to the outermost point where the plates terminate and the bristles commence. No. 1. Female. Left all black ; on the right side, the first slightly lighter colour. Left side 328 plates. Right side 324 plates. Length of no. no. no, no, no. 50 100 150 200 250 millim. 460 590 520 420 240 No )) 50 100 150 200 250 millim. .. 430 .. 560 .. 510 .. 420 .. 240 No. 3. Female. All black. Left side 334 plates. millim. Length of no. 50 430 no. 100 520 no. 150 490 no. 200 380 no. 250 180 Eight side 328 plates. No. 50 „ 100 „ 150 „ 200 „ 250 millim. .. 450 .. 540 .. 470 .. 370 .. 210 Left side 318 plates. Length of no. 50 Male. All black. Right side 321 plates. millim. ,.. 490 no. 100 640 no. 150 590 no. 200 420 no. 250 250 No. 50 „ 100 „ 150 „ 200 „ 250 millim. .. 480 .. 630 .. 590 .. 440 .. 250 Another example (sex unknown). All black. Left side 333 plates. No. 50 „ 100 „ 150 „ 200 „ 250 millim. .. 450 .. 570 .. 520 .. 400 .. 250 Right side 339 plates. No. 50 „ 100 „ 150 „ 200 „ 250 millim. ,. 500 ,. 600 . 560 . 450 . 240 |