ISOPODS OF WORTH AMERICA. 



15 



The first segment of the thorax is united with the head to form a 

 carapace. The second or first free segment is the shortest of all; the 

 third and fourth or second and third free segments are nearly equal in 

 length, the third being perhaps a little longer; the fifth and sixth or 

 fourth and fifth free segments are subequal and are the longest; the 

 sixth or seventh free segment is about equal in length to the third free 

 segment. 



The abdomen is composed of six segments. The first three are sub- 

 equal in length and carry on the ventral side three pairs of well- 

 developed pleopoda. The two following segments are subequal, and 

 each is about one-half as long as any of the three preceding segments 

 and about one-half as wide, being abruptly narrower. These seg- 

 ments do not carry pleopoda. There are thus only three pairs of 



FIG. 16. TANAIS 



NO R M ANI . 



x Hi. 



FIG. 17. TANAIS NORMANI. FIRST 

 GNATHOPOD. X 44. 



FIG. 18. TANAIS NORMANI. a, FIRST 



ANTENNA. X 44. b, SECOND ANTEN- 

 NA. X 44. 



pleopoda. The sixth or terminal segment is as wide as the two pre- 

 ceding segments and is rounded posteriorly. The uropoda are single 

 branched; the peduncle is followed by a five-articulate branch. 



The first pair of legs or gnathopods are chelate; the following six 

 pairs of legs are ambulatory. 



Only three specimens of this species were collected by Mr. Harold 

 Heath at Monterey Bay, California. 



The types are in the U. S. National Museum. Cat. No. 30615, 

 U.S.N.M. 



This species differs from Tanais alascensis Richardson in having the 

 abdomen composed of six segments, while in T. alascensis it is com- 

 posed of five segments; in having the uropoda composed of a peduncle 



