NO. i3r,o. NATURAL HISTORY OF THE ISOPODA— RICHARDSON. 



77 



Pig. 6.'>.— Ioni 

 T H o M p s o N I , 



MAXILLIPED. 



The seven pairs of legs are all similar, and terminate in a pi-ehen- 

 sile 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. Antennas conspicuous, six jointed. An- 

 tennuhe, three jointed. The segments of the abdomen 

 are distinct, all six furnished each with a pair of elon- 

 gated leaf-like tapering appendages. 



Two specimens were collected ))y Mr. G. M. Gray at North Falmouth, 

 Massachusetts. They were found on CkilUanassa t<tl)iipsonL 



The species is named for Mr. Millett T. 

 Thompson, from whom the specimens were 

 received. 



Ty2)e.—C^t. No. 29091, U.S.N.M. 

 This species is apparently very close to 

 I. cornuta^ Spence Bate, from Vancouver 

 Island. It agrees with I. cornuta in the ab- 

 sence of the elongated epimeral lobes (lames 

 pleurales), in which both species diifer from 

 I. thoracica (Montagu). lone t/iompsont and 

 I. cornuta are both much larger species than 

 In the description of 1. cornuta^^ the author savs 



Fig. 66.— Tone thompsoni, first 

 lamella of maksupium. xlo. 



Fig. 67.— Ion e thomp- 

 soni, LEG OF SIXTH PAIR 

 OF ADULT FEMALE. Xllj. 



I. thoracica 



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 / 



tliom;pmni., in which the epimera of the three 



posterior thoracic segments are smaller than 

 those of the anterior segments, 

 although thej'^ occupy the en- 

 tire lateral margin, and they 

 are rounded posteriorly 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 /. thompsoni^ these lateral 

 processes or lobes extend out straight at the sides. 

 Bate and Westwood, in describing L cornuta^ state 

 that the last pair of inner saccular branches of the 

 pleo])oda are almost obsolete. There arc but four 

 pairs of inner branches in /. thompmnL The above 



quoted authors also describe the inner branches of the pleopoda as 



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



?- British Sesssile-i'vcd Crustacea, II, 1867, p. 254. 



Fig. fis.— Tone thomi 



SOM, MALE. X K. 



