288 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS EXOSPH.EROMA. 



it. Body widening gradually from the head backward. Thorax transversely ridged 

 and provided with three longitudinal rows of small tubercles. Branches of 



uropoda very large, expanded KxoxpJuvroma ampllccmda (Stimpson) 



a^. Body not increasing in width from the head l^ackward. Surface of thorax 

 smooth. Branches of uropoda not expanded. 

 h. Extremity of terminal abdominal segment produced in a rhomboid process. 



Exosphirroina rhomhunnn (Richardson) 

 I/. Extremity of terminal abdominal segment not produced in a rhomboid -process, 

 c. Surface of abdomen with tubercles. 



d. Abdomen posteriorly ending in a triangular apex, on either side of which is 

 a small tooth. 

 e. With three tubercles at base of terminal abdominal segment. Outer 

 branch of urojwda not longer than inner branch and both shorter than 

 terminal segment of abdomen. Outer branch not acutely i)roduced. 



Exosplnvroma yucatanum (Richardson) 



e^. With two tubercles at base of terminal abdominal segment. Outer 



branch of uropoda extending beyond the inner branch, a distance equal 



to half the length of the inner branch. Outer branch very acute at 



extremity Exosphseroma faxoni, new species 



d''. Abdomen posteriorly rounded. With eight tubercles, six on terminal seg- 

 ment and two on preceding segment. 



ExospJurronia octoncum (Richardson) 

 c^. Surface of abdomen without tubercles. 



d. Outer branch of uropoda smooth on exterior margin. 



e. Outer branch of uropoda half as long as inner branch and half as wide. 



Exosphseroma thermophilum (Richardson) 

 e\ Outer branch of uropoda more than half as long as inner branch. 

 /. Outer branch four-fifths as long as inner branch and half as wide. 



Exoi<ph:vroina dugesi (Dollfus) 

 f. Outer ))ranch two-thirds as long and as wide as inner branch. 



Exoitphuroma oregonensis (Dana) 

 d^. Outer branch of uropoda crenulated on exterior margin. 



Exosphxroma crenulatum (Richardson) 



EXOSPHiEROMA AMPLICAUDA (Stimpson). 



Sphasroma amplicauda Stimpson, Bost. Jour. Nat. Hist., VI, 1857, p. 510. — 

 Richardson, Proc. U. S. Nat. Mus., XXI, 1899, p. 835; Ann. Mag. Nat. 

 Hist. (7), IV, 1899, !>. 179; Amer. Naturalist, XXXIV, 1900, p. 222. 



Localities. — Tomales Ba}", California; Ky.ska Harbor, Alaska; north 

 coast of Arachitka, Alaska; Monterey Bay, California. 



Found in low water on beach. 



Body narrower anteriorly than posteriorly, oradually increasing in 

 width from the head to the abdomen, a little more than one and a 

 half times longer than broad, 5 mm.: 8 mm. 



Head a little more than twice as wide as long, with a frontal l)order 

 arising between the eyes, which is produced in a small median point. 

 The eyes are small, round, composite, and situated in the post-lateral 

 angles of the head. The first pair of antenna^ have the basal article 

 long and equal in length to the third; the second article is half as 

 long as either of the other two. The flagellum is composed of tive 



