NEMERTEANS 



between" and beside the rectangular marks for the white ground color. 

 They are often decidedly irregular in shape, but in ordinary states of 

 contraction of body average about one and a half times as long as 

 broad, and are separated medially by a space about half as great as 

 their transverse diameters. In addition to the sixteen pairs of rectangu- 

 lar marks, a pair of slender, irregular, brown lines are situated near 

 the lateral margins along the whole length of the body behind the head. 

 Anteriorly these slender brown lines join the more anterior rectangular 

 markings, but at about the third pair of rectangular markings become 

 separated, to join again at about the fourteenth pair. When the 

 animal is slightly compressed, a narrow white margin appears out- 

 side these lateral brown lines. The fusion between the first pair of 

 rectangular markings and the lateral lines is usually complete, while the 

 second pair is often joined by only narrow bridges of the brown color 

 (text fig. 21 ). Sometimes other pairs of markings are connected with 

 the lines by similar bridges of color, and toward the end of body this 

 is usually the case. At about the fourteenth pair of markings there is 

 often a complete fusion of brown color, both of the lateral lines and 

 of the rectangular markings of the same pair, and very commonly 

 only a narrow, transverse band of white serves to indicate the division 

 between the fourteenth and fifteenth, and between the fifteenth and 

 and sixteenth, or last, markings. Often even this narrow transverse 

 white band does not extend more than half way to the margins of the 

 body. This fusion of all the brown markings is commonly limited 

 to the three or four posterior pairs of markings, but in some individuals 

 involves the greater portion of the dorsal surface. When carried to 

 the extreme condition all the markings on the body back of the head 

 are united, and this fusion gives rise to the second and less common 

 variety. 



In this second variety (pi. xiv, fig. 8) the whole dorsal surface back 

 of the head is of a deep brown color interrupted by about fifteen irreg- 

 ular, transverse, whitish bands reaching laterally toward margins of 

 body. These fifteen whitish bands indicate the spaces between the 

 sixteen pairs of rectangular markings described for the first variety. 

 The lateral lines have become fused and lost in the rectangular mark- 

 ings, and both markings of the same pair have completely lost their 

 individuality. Occasionally, however, a paler median line is indicated. 

 Laterally, too, the adjacent pairs of markings have fused completely. 

 Often the transverse whitish bands do not extend more than half way 

 to the lateral margins, as was mentioned in regard to the caudal region 

 of the first variety. They often become indistinct, and gradually shade 



