North American Species of Diaptomus. 133 



Diaptomus sanguineus Forbes. (Pis. XXIII., XXIV., 

 and XXV.) 



Diaptomus sanguineus, Forbes, '76. pp. 15, 16, 23, Fig. 24, 28-30. 



Diaptomus sanguineus, Forbes, '82a, p. 647. PI. VIII., Fig. 1-7, 13. 



Diaptomus armatits(?), Herrick. '82, p. 223. Fig. 1, a, b. 



Diaptomus armatus^?), Herrick, '84, p. 139. 



Diaptomus sanguineus, Herrick, '84, p. 138, PI. Q, Fig. 12. 



Diaptomus minnetonka, Herrick, '84, p. 138, PI. Q, Fig. 8-10. 



Diaptomus sanguineus, de Guerne et Richard, '89b, p. 20, Fig. 9-11 ; 



PI. IV., Fig. 24. 

 Diaptomus sanguineus, Marsh, '93, p. 195, PI. III.. Fig. 1-3. 



A rather large species, one fourth to one third as wide as 

 long. The cephalothorax widens gradually to the third seg- 

 ment (being broadest at the suture between that segment and 

 the fourth), then narrows less gradually to the abdomen. In 

 the male the thorax is less uniform in breadth than in the 

 female. The last cephalothoracic segment is greatly pro- 

 duced on each side laterodorsally and bears a large spine, 

 slightly swollen at the base, varying in length from that of 

 the segment to one fourth its length. On the same segment 

 and midway between the outer spine and the abdomen is 

 another broader and shorter spine. Both of these spines are 

 slightly curved. In the female (PL XXIV., Fig. 3) they are 

 generally quite noticeably larger than in the male. On 

 the first abdominal segment is still another spine, slightly 

 outcurved and pointing outward, about as large as the sec- 

 ond of the spines mentioned above. In the female the 

 penultimate cephalothoracic segment bears a dorsal hump at 

 its anterior margin (PI. XXIV., Fig. 5, 6). This is wanting 

 in the male. The abdomen is produced dorsally and ven- 

 trally at the anterior part, making it look like a keel (PI. 

 XXIV., Fig. 1, 2), the keel being most pronounced on the 

 ventral side. The egg-mass is large and elliptical, with the 

 major axis transverse to the body. 



Antennae 25-segmented, the seventeenth or eighteenth seg- 

 ment reaching about to the base of the abdomen. The right 

 male antenna is thickly swollen beyond the geniculate joint. 

 The last two segments have no special armature, but the 

 antepenultimate one (PI. XXIII., Fig. 6-8) is armed at the 



