TSOPODft OF NORTH AMERICA. 827 



as wide at its anterior end as it is at its posterior extremity; it 

 measures 2 mm. in width at tlie anterior portion and only 1 mm. at the 

 posterior end. 



The abdomen is composed of two seg-ments, the tirst one of Avhich is 

 short and narrow. Tiie terminal segment has the lateral margins pro- 

 duced on either side in two angular processes, one at the base of the 

 segment and the other a little below the middle. The segment termi- 

 nates in an acute point. There is also a median tubercle on each one 

 of the abdominal segments, the tubercle on the terminal segment being 

 situated at the base of the segment. 



The marsupial plates arc covered with small tul)ercles. 



35. Genus ARCTURUS Latreille. 



Body slender, somewhat cylindrical in form, with the fourth seg- 

 miMit of the thorax not greatly longer than the others. Epimera small 

 l)ut ilistinct on all the thoracic segments with the exception of the 

 tirst. Marsupium of female composed of three pairs of ])lates issuing 

 from the second, third, and fourth segments. A})domen composed of 

 three segments, two segments anterior to the large terminal one. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS ARCTURUS. 



a. End of terminal segment notched, as seen from above. 



h. Body smooth and free from s])in('S Arcturns l>erinf)<iiniK Benedict 



//. Body spiny Arcturiin loii(jixj)inis Benedict 



f/. End of terminal abdominal segment withont notch. 



b. Body withont spines or tubercles, perfectly smooth and glabrous. 



Arcturu.'< glaher Beiiedict 

 h\ Body with spines or tubercles. 



c. Terminal segment of abdomen armed with a long median terminal si)ine, pro- 

 jecting beyond the end of the segment. 

 d. Head with two spines. Second joint of second pair of antenna' armed with 

 one spine at upper end. Thorax with few spines. Surface of terminal 

 abdominal segment smooth. 

 e. Second joint of peduncle of second pair of antenna' without sj)inc at base 

 on outer margin. First pair of antennae extending one-third the length 

 of the third joint of second pair of antennpe. Dorsal spines wanting on 

 second abdominal segment. Spines wanting on opercular valves. 

 Anterior thoracic appendages furnished with a number of spines on 



the proximal joints ArdKrufi piirjnireus Beddard 



e^. Second joint of peduncle of second pair of antenn;e with spine at base on 

 outer margin. First ])air of antenn;e extending two-thirds the length 

 of the third joint of second pair of antenna'. Dorsal spines present on 

 second abdominal segment. Spines present on opercular valves. 

 Anterior thoracic appendages without spines except on penultimate 



joint Arctunis caribba-u>< Richardson 



d\ Head with eight spines. Second joint of second pair of antenna? armed 

 with three spines at the upper end. Thorax with many spines. Sur- 

 face of terminal abdominal segment with three rows of spines on dorsal 

 surface. Row of spines on each opercular valve. 



Aniurnx Jforidanus Richardson 



