an osculant Genus of Crustacea. 73 



by an acute process, without any lateral swimming-apparatus, and 

 exhibits at its base rudiments of an incipient articulation : more- 

 over, there also appear traces of articulation at the base of the acu- 

 minate terminal portion of the joint ; whence it is evident (as well 

 as from the circumstance of there existing five sets of subabdominal 

 respiratory plates,) that the abdomen consists of the ordinary num- 

 ber of segments, more or less soldered together, each of which pos- 

 sesses its own appendages as in the more developed types of the sec- 

 tion. 



The male is about 5 lines long, and the female nearly 10, exclu- 

 sive of antennae. 



The specimens of this insect figured by Mr. Sowerby were caught 

 by Mr. T. W. Simmons entangled in nets off Dysart, near Inch- 

 keith. 



Its appearance is so remarkable that the head may often be mis- 

 taken for the tail, especially if the antennae are hidden. Sometimes 

 it assumes the appearance of a tumbler or posture-master ; and at 

 times the abdomen is recurved beneath the thoracic portion. 



The eggs are red, and adhere to the underside of the largest seg- 

 ment of the body. 



Of its habits we are entirely ignorant, as well as of its motions, 

 which, from the peculiar formation of the legs, must be curious. 



DESCRIPTION OF PLATE IX. 



Fig. 1. Arcturus longicornis $ , magnified. The two outlines below exhibit the 

 natural length of the male and female (the former being the smaller). 

 2. One of the inner antenna. 3. The extremity of one of the outer 



antennas. 4. The lip. 5. One of the mandibles. 6. One of the 



inner maxillfe. 7. One of the second maxillae. 8. The outer lobe 



seen in another position. 9. One of the foot-jaws. 10. One of the 



first pair of legs. 11. One of the six following legs. 12. One of 



the six posterior legs. 13. The front of the body seen sideways. 



14. The large thoracic segment of the female seen beneath, showing the 

 subthoracic pouch. 15. One of the ova, highly magnified. 16. The 

 abdomen seen from beneath, with the outer valves of the respiratory ap- 

 paratus closed. 17. One of the outer valves detached. 18. One 

 of the external respiratory plates. 18 a. The same, more magnified. 

 18 6. One of the curved basal lateral appendages, still more magnified. 

 18 c. Part of one of the terminal feathered hairs. 19. One of the 

 second pair of respiratory plates. 19c!. The same, more highly mag- 

 nified. 20 and 20 «. One of the third pair of ditto. 2 1 and 2 1 a. One 

 of the fourth pair of ditto. 22. One of the fifth ditto. 23. One of a 

 pair of internal organs above described in the $ , and supposed to be con- 

 nected with the organs of generation. 



