314 DESCRIPTIONS OF PARASITIC COPEPODA. 



essentially alike in all the specimens e^ftmined. Four figures are given, 

 two from sand-shark specimens, and one each from the dog-fish and At- 

 wood's shai'k; these serve to represent the principal differences ob- 

 served. Tlie basal joint is very large, with a notch of variable size on 

 the outer margin. The rami are larger in the sand-shark specimens 

 than in those from the other species, and there is considerable variation 

 in their outline; the outer ramus has four spines at the outer end. with 

 sometimes a smaller one on the outer margin, slightly in advance of the 

 latter; a small curved spine also projects from the same margin near the 

 middle. The inner ramus is without spines. lu Pandarus bicolor, the 

 fourth pair of feet are quite unlike those of this species, the rami being 

 much longer, more slender, and of an entirely different shape. 



The ventral caudal plate is shorter than the dorsal, and slightly con- 

 cave along the middle of the posterior margin. 



There is considerable variation in the color of this species. In alco- 

 holic specimens the prevailing color of the dorsal surface of the first 

 four segments is a dull yellow, or yellowish white ; the fifth segment is 

 sometimes of the same color, but generally darker, and with a grayish 

 or brownish tinge ; the caudal plate is nearly white, or slightly yellow- 

 ish. In most specimens there are two bright-brown or brownish-black 

 spots close to the front margin, one on each side. These often extend 

 backward a variable distance, and sometimes unite in front to form a 

 horseshoe-shaped figure, which may cover a greater or less extent of 

 surface. The dorsal lobe of the fourth segment is generally marked 

 with the same color, which may form a central dot, nearer the posterior 

 than the anterior margin, or a broad blotch covering the greater part 

 of the lobe. Specimens from the dog-fish are usually darker than those 

 from the sand-shark or Atwood's shark, and the brown or blackish mark- 

 ing often covers most of the first segment, leaving only an elongate 

 median light space of variable width. The same markings frequently 

 extend to the lobes of the second and third segments, and that of the 

 fourth segment is generally entirely dark. 



The length of the body, exclusive of the ovigerous tubes, is between 

 7mm ami j^mm^ nearly all the specimens collected coming within those 

 dimensions. The drawings of appendages representing this species on 

 plates VI and VII have been made from alcoholic preparations, mostly 

 treated with a dilute solution of caustic potash, and examined under 

 very slight pressure. 



This species is found attached to the surface of the body and to the 

 fins. It has been most commonly taken from the sand shark, which is 

 abundant in Vineyard Sound, Massachusetts, but is frequently found on 

 the dog-fish in the same region. It has been collected only once from 

 Atwood's shark, but this species of shark has not been observed since 

 1875. The specimens recorded in the following list were all obtained 

 by the U. S. Fish Commission. 



