568 



fused with the basipodite but in some species their indistinct division has 

 been observed. The telson is not fused with the last urosomite. 

 Type species: Amphithyrus bispinosus Claus, 1879. 



KEY TO SPECIES OF GENUS AMPHITHYRUS 



1. Coxal plates V spiniform, acute and directed backward 



I. A. bispinosus Claus. 



— Coxal plates V usual, not spiniform 2. 



2. Body surface without sculpture, smooth. Distal process of 5th seg- 

 ment of pereopods II almost reaches tip of denticle on posterior mar- 

 gin of 6th segment 4. A. glaber Spandl. 



— Body surface with reticulate or striate sculpture. Distal process of 

 5th segment of pereopods n not reaching even base of denticle on 

 posterior margin of 6th segment 3. 



3. Pereopods VII with three-five rudimentary distal segments. Basi- 

 podites and rami of uropods sculptured 5. A. sculpturatus Claus. 



— Pereopods VII without distal segments or with single rudimentary 

 one. Basipodites and rami of uropods not sculptured 4. 



4. Telson galeiform, with acuminate tip, and about twice as long as last 

 urosomite. In pereopods I and II notch between denticle and posterior 

 margin of 6th segment smoothly rounded 2. A. similis Claus. 



— Telson with rounded tip, shorter than last urosomite. In pereopods I 

 and II notch between denticle and posterior margin of 6th segment 

 angular 3. A. muratus Volkov sp. n. 



1. Amphithyrus bispinosus Claus, 1879 (Fig. 246) 



Claus, 1879b: 15; 1887: 41; Stebbing, 1888: 1489; Spandl, 

 1927: 247. 



Length of adult individuals 3.5-4 mm. 



The body is high, compact, and markedly curved dorsoventrally. All 

 the somites of the body, the telson, the coxal plates, the 2nd segment of 

 pereopods V and VI, and the basipodites of the uropods have a distinct 

 sculpture in the form of longitudinal furrows or polygons. 



Pereopods I and II are short and weak. The 2nd segment of pere- 

 opods I is barely bulged distally and its anterior margin barely curved or 

 straight; the 3rd-7th segments together are equal in length to the 2nd; the 

 4th and 5th segments are equal in length and the 4th is not broader than 

 the 5th; the distal process of the 5th segment is shorter than half the 6th 

 segment. The 2nd segment of pereopods II has a concave anterior margin 

 and bulged posterior one; the 3rd-7th segments together are shorter than 

 the 2nd; the 4th segment is broader than the 5th; the distal process of the 

 5th segment reaches the tip of the denticle on the posterior margin of the 



