510 



BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



FIG. 555. ION E 

 THOMPSONI. 

 MAXILLIPED. 



FIG. 556. lONE THOMPSONI. FIRST 

 LAMELLA OF MARSUPIUM. X 10. 



hand. There are two expansions or carinse on the basis of all the 

 legs, the anterior one being only half as long as the other. 



Male with all the segments of the thorax distinct. Eyes wanting. 

 Antenna? conspicuous, six jointed. Antennulae, three jointed. The 

 segments of the abdomen are more or less distinct, all six furnished 

 each with a pair of elongated leaf - 

 like tapering appendages. 



Two specimens were collected 

 by Mr. G. M. Gray at North Fal- 

 mouth, Massachusetts. They 

 were found on Callianassa stimp- 

 soni. 



The species is named for Dr. 

 Millett T. Thompson, from whom the speci- 

 mens were received. 



Type. Cat. No. 29091, U.S.N.M. 

 This species is apparently very close to 7. cornuta Spence Bate, 

 from Vancouver Island. It agrees with I. cornuta in the absence of 

 the elongated epimeral lobes (lames pleurales), in which both species 

 differ from 7. thoracica (Montagu). lone thompsoni and /. cornuta are 

 both much larger species than 7. thoracica. In the description of /. 

 comuta, a the author says that the coxae of the three posterior segments 

 of the thorax are larger than the four anterior, and are produced 

 posteriorly to a point. This is 

 not true of I. thtfnipsoni, in 

 which the epimera of the three 

 posterior thoracic segments are 

 smaller than those of the ante- 

 rior segments, although they 

 occupy the entire lateral mar- 

 gin, and they are rounded pos- 

 teriorly and not produced to a 

 point. Spence Bate also speaks, in reference to /. 

 cornuta, of the antero- lateral "horn-like process of 

 the cephalon* curving posteriorly." In 7. thomp- 

 soni, these, lateral processes or lobes extend out 

 straight at the sides. Bate and Westwood, in describing I. cornuta, state 

 that the last pair of inner saccular branches of the pleopoda are almost 

 obsolete. There are but four pairs of inner branches in 7. thompsoni. 

 The above quoted authors also describe the inner branches of the 

 pleopoda as gradually diminishing in size to the last pair, whereas 

 the outer branches gradually increase in size. This is not true of 

 7. thompsoni. 



FIG. 557. lONE THOMPSONI. 

 LEG OF SIXTH PAIR OF 

 ADULT FEMALE. X llj. 



FIG. 558. lONE THOMP- 

 SONI., MALE. x8. 



a Proc. Zool. Soc. London, 1864, p. 668. 



& British Sessile-eyed Crustacea, II, 1868, p. 254. 



