Padfic Coast of North America. 27-3 



Fourth segment of thorax not greatly longer than otliers. 

 Marsupium of female composed of four pairs of plates. Pos- 

 terior thoracic legs biunguiculate. 



Analytical Key to the Species o/ Arcturus *. 



a. End of abdomen notched as seen from 

 above. 

 b. Body smooth and free from spines . . 61. A. berinyanus, Benedict. 

 b'. Body spiny. 



c. Head and six sefynieuts of thorax 

 each with a pair of spines on the 

 dorsum. Second and third articles 



of antennjie without spines 6_'. A. lonjispinis, Benedict. 



c'. Head and segments of thorax with 



not less thin two pairs of spines 



to the segment. 



d. Head wifh one large median spine 



on anterior part of head in front 



of eyes 63. A. intennedius, sp. n. 



d'. Head with three spines on ante- 

 rior part of head in front of eyes. 64. A. Murdochi, Benedict. 

 a . End of abdomen without notch 6o. A. ylaber, Benedict. 



61. Arcturus berincjanaSj 13eiiedict. 



Arcturns heringanus, Benedict, Proc. Biol. Soc. Washington, xii. 18S)8, 

 pp. 46, 47. 



Hah. Alaska ; Bering Sea. 



62. Arcturus longispinis, Benedict. 



Arcturus lojiffispinis, Benedict, Proc. Biol. Soc. Washington, xii. 1898, 

 pp. 44, 45. 



I/ab. Aleutian Islands. 



63. Arcturus intermedins, sp. n. 



Head with a deep excavation on its anterior margin, the 

 antero-lateral angles being produced in a double process, the 

 inner one rounded, the outer one acutely pointed. Near the 

 anterior margin in the median line is one large spine. Just 

 back of the eyes and between them are two long spines. Tiie 

 lateral margins of the head are produced in two small angu- 

 lations, with a rounded sinus between, posterior to the double 

 antero-lateral process. On the post-lateral margin on eitlier 

 side of the head is a small spine. 



The first pair of antenna are small and short, not reaching 



* Dr. Benedict's key is used in part for the genus Arcturuf. Proc. 

 Biol. Soc. Washington, xii. (1898) pp. 42, 43. 



